Elizabeth G Boulding | University of Guelph (original) (raw)

Papers by Elizabeth G Boulding

Animals living in intertidal habitats experience high temperatures and low humidity during emersi... more Animals living in intertidal habitats experience high temperatures and low humidity during emersion that represent extreme deviations from those experienced during immersion; some use behaviour to ameliorate these stressors. We made in situ observations of 3 behaviours displayed by the Pacific intertidal snail Littorina subrotundata on 3 exposed rocky intertidal shores in the northeast Pacific: microhabitat selection, activity level, and conspecific aggregation. We hypothesized that these behaviours might be altered in response to temperature and/or humidity at a particular time during tidal emersion. We used the Akaike information criterion to compare a set of models for each of the 3 behaviours that included combinations of substrate temperature (T s ), vapour pressure deficit (VPD) (which encompasses humidity), emersion time, snail shell width (Size), and study site (Site) as the independent variables. The best supported model of microhabitat selection in the summers of 2011 and 2012 used only the independent variables Site and Size. The best supported model of activity included both T s and VPD in 2011 but included only T s in 2012; increased T s resulted in decreased activity. None of the models in the set explained much of the variance in conspecific aggregation. We conclude an alternate cue for microhabitat selection is likely in this system and suggest that biogenic refuges created by barnacles are a likely driver. Our findings also suggest that thermal stress during emersion is the primary cue that informs the snails to reduce their activity.

Comparative genome scans can be used to identify chromosome regions, but not traits, that are put... more Comparative genome scans can be used to identify chromosome regions, but not
traits, that are putatively under selection. Identification of targeted traits may be more
likely in recently domesticated populations under strong artificial selection for
increased production. We used a North American Atlantic salmon 6K SNP dataset to
locate genome regions of an aquaculture strain (Saint John River) that were highly
diverged from that of its putative wild founder population (Tobique River). First,
admixed individuals with partial European ancestry were detected using STRUCTURE
and removed from the dataset. Outlier loci were then identified as those showing
extreme differentiation between the aquaculture population and the founder
population. All Arlequin methods identified an overlapping subset of 17 outlier loci,
three of which were also identified by BayeScan. Many outlier loci were near candidate
genes and some were near published quantitative trait loci (QTLs) for growth, appetite,
maturity, or disease resistance. Parallel comparisons using a wild, nonfounder
population (Stewiacke River) yielded only one overlapping outlier locus as well as a
known maturity QTL. We conclude that genome scans comparing a recently
domesticated strain with its wild founder population can facilitate identification of
candidate genes for traits known to have been under strong artificial selection

The intertidal snail Littorina saxatilis has repeatedly evolved two parallel ecotypes assumed to ... more The intertidal snail Littorina saxatilis has repeatedly evolved two parallel ecotypes assumed to be wave adapted and predatory shore crab adapted, but the magnitude and targets of predator-driven selection are unknown. In Spain, a small, wave ecotype with a large aperture from the lower shore and a large, thick-shelled crab ecotype from the upper shore meet in the mid-shore and show partial size-assortative mating. We performed complementary field tethering and laboratory predation experiments; the first set compared the survival of two different size-classes of the crab ecotype while the second compared the same size-class of the two ecotypes. In the first set, the large size-class of the crab ecotype survived significantly better than the small size-class both on the upper shore and in the laboratory. In the second set, the small size-class of the crab ecotype survived substantially better than that of the wave ecotype both on the upper shore and in the laboratory. Shell-breaking predation on tethered snails was almost absent within the lower shore. In the laboratory shore crabs (Pachygrapsus marmoratus) with larger claw heights selected most strongly against the small sizeclass of the crab ecotype, whereas those with medium claw heights selected most strongly against the thin-shelled wave ecotype. Sexual maturity occurred at a much larger size in the crab ecotype than in the wave ecotype. Our results showed that selection on the upper shore for rapid attainment of a size refuge from this gape-limited predator favors large size, thick shells, and late maturity. Model parameterization showed that size-selective predation restricted to the upper shore resulted in the evolution of the crab ecotype despite gene flow from the wave ecotype snails living on the lower shore. These results on gape-limited predation and previous ones showing size-assortative mating between ecotypes suggest that size may represent a magic trait for the thick-shelled ecotype.

Oceanography and Marine Biology - An Annual Review, 2015

Journal of Molluscan Studies, 2015

Journal of Evolutionary Biology, 2007

Prey populations after a predator invasion 1987 ª 2 0 0 7 T H E A U T H O R S . J . E V O L . B I... more Prey populations after a predator invasion 1987 ª 2 0 0 7 T H E A U T H O R S . J . E V O L . B I O L . 2 0 ( 2 0 0 7 ) 1 9 7 6 -1 9 8 7 J O U R N A L C O M P I L A T I O N ª 2 0 0 7 E U R O P E

BMC Genomics, 2012

Background: Geographical isolation has generated a distinct difference between Atlantic salmon of... more Background: Geographical isolation has generated a distinct difference between Atlantic salmon of European and North American Atlantic origin. The European Atlantic salmon generally has 29 pairs of chromosomes and 74 chromosome arms whereas it has been reported that the North American Atlantic salmon has 27 chromosome pairs and an NF of 72. In order to predict the major chromosomal rearrangements causing these differences, we constructed a dense linkage map for Atlantic salmon of North American origin and compared it with the well-developed map for European Atlantic salmon. Results: The presented male and female genetic maps for the North American subspecies of Atlantic salmon, contains 3,662 SNPs located on 27 linkage groups. The total lengths of the female and male linkage maps were 2,153 cM and 968 cM respectively, with males characteristically showing recombination only at the telomeres. We compared these maps with recently published SNP maps from European Atlantic salmon, and predicted three chromosomal reorganization events that we then tested using fluorescence in situ hybridization (FISH) analysis. The proposed rearrangements, which define the differences in the karyotypes of the North American Atlantic salmon relative to the European Atlantic salmon, include the translocation of the p arm of ssa01 to ssa23 and polymorphic fusions: ssa26 with ssa28, and ssa08 with ssa29.

Journal of Evolutionary Biology, 2010

Hydrobiologia, 1998

We investigated whether measurements of barnacle microtopography could be used as covariates to i... more We investigated whether measurements of barnacle microtopography could be used as covariates to increase precision in randomised field experiments with intertidal Littorina populations. We used image analysis to quantify the microtopography of the barnacles within 100 cm 2 quadrats in July 1994 using as variables: number of barnacles, number of dead empty barnacles, mean distance to nearest neighbouring barnacle, total area covered by barnacles, and number of pockets of different size-classes [extra-small (< 0.15 cm 2 ), small (≥ 0.15 and < 0.30 cm 2 ), medium (≥ 0.30 and < 0.45 cm 2 ), large (≥ 0.45 and < 0.60 cm 2 ), and extra-large (≥ 0.60 cm 2 )] at least 75% surrounded by barnacles. We then used these variables to predict the abundance of Littorina spp. in the same quadrat. Two variables: the number of extra-small pockets and the number of small pockets accounted for 50% of the variation in total littorinid snail abundance among quadrats for January 1995 and for 47% of the variation for August 1994 but for only 16% of the variation for June 1994. However the single variable, the number of barnacles, accounted for 29-36% of the variation in snail abundance on these dates and can be measured without special equipment. The best combination of covariates was the number of extra-small pockets alone. The number of extra-small pockets between barnacles may be influencing the snail abundance by providing a refuge from wave shock and heat stress/desiccation. We suggest that the availability of these refuges among the barnacles could act as a density-dependent regulator of the total population size of a particular species of Littorina.

Integrative and Comparative Biology, Jan 1, 2010

BMC Genomics, Aug 28, 2012

Background: Geographical isolation has generated a distinct difference between Atlantic salmon of... more Background: Geographical isolation has generated a distinct difference between Atlantic salmon of European and North American Atlantic origin. The European Atlantic salmon generally has 29 pairs of chromosomes and 74 chromosome arms whereas it has been reported that the North American Atlantic salmon has 27 chromosome pairs and an NF of 72. In order to predict the major chromosomal rearrangements causing these differences, we constructed a dense linkage map for Atlantic salmon of North American origin and compared it with the well-developed map for European Atlantic salmon. Results: The presented male and female genetic maps for the North American subspecies of Atlantic salmon, contains 3,662 SNPs located on 27 linkage groups. The total lengths of the female and male linkage maps were 2,153 cM and 968 cM respectively, with males characteristically showing recombination only at the telomeres. We compared these maps with recently published SNP maps from European Atlantic salmon, and predicted three chromosomal reorganization events that we then tested using fluorescence in situ hybridization (FISH) analysis. The proposed rearrangements, which define the differences in the karyotypes of the North American Atlantic salmon relative to the European Atlantic salmon, include the translocation of the p arm of ssa01 to ssa23 and polymorphic fusions: ssa26 with ssa28, and ssa08 with ssa29.

Journal of …, Jan 1, 2001

The pile perch, Rhacnchilus vacea (Embiotocidae). is abundant on the Pacific Coast of North Ameii... more The pile perch, Rhacnchilus vacea (Embiotocidae). is abundant on the Pacific Coast of North Ameiica and is known to crush hard-shelled prey with its heavy pharyngeal teeth. We investigated whether pile perch predation has the potential to limit or regulate populations of Littorina .<iitkana, a direct-developing gastropod found on wave-sheltered shores near Bamfield, British Columbia. Canada. Laboratory experiments showed that pile perch required an average of only 19.2 sec (SE = 5.61: « = 20) to crush and swallow a large L. silkami. which resulted in consumption rates averaging 33.3 (SE = 6.27; n = 4) large snails per day. The snails had no size refuge from predation by adult fish because even small fish (fork length 21 cm) could crush the largest L sitkana present on the shore (>1 1 mm shell width). Indeed, some fish showed a significant preference for large snails {shell width >6.3 mm) over small snails (3.35 mm < shell width < 4.0 mm). Our 1998 observations with SCUBA during daytime high tides showed that the density of pile perch foraging in the intertidal averaged 0.1 19 (SE = 0.0205; n = 20) individuals per square meter (estimated fork lengths 5^0 cm). However, the intertidal distribution of pile perch that were actually consuming prey was highly aggregated. In the field, we investigated whether predation by this fish on snails deployed onto boulders was density dependent. The fish swam parallel to the shore and located and consumed 4()'/f of the patches of L. siikiiiui that we deployed (;? = 70) within 50 min. This foraging behavior resulted in density-dependent predation on the deployed snails in only one of the three tidal cycles (or 2 of the 12 days) of our experiment. We offer several proximate reasons for the low frequency of density-dependent predation found in this study and conclude that the pile perch may not be an important regulating factor for L. siikiiiui populations at this site at the present time. However, the very high predation rates we observed suggest that this predatory fish is an important limiting factor at this site.

Conservation Genetics, Jan 1, 2012

Journal of …, Jan 1, 2001

Sibling specie.s Litwrina sculidciui and L. plena are difficult to distinguish in the field. Here... more Sibling specie.s Litwrina sculidciui and L. plena are difficult to distinguish in the field. Here we present a new molecular liiul and use it lo evaluate the discrete and quantitative morphological characters that have been proposed as diagnostic. We collected 38.5 snails of both species from 1 1 sites in Washington state and used restriction enzyme digestion of a PCR-amplified, 480 bp fragment of the mitochondrial cytochrome b gene to distinguish the species. This new molecular assay produces species-specific restriction fragment patterns that correspond with identification of males by penis morphology. To evaluate the usefulness of morphological characters, we scored three discrete shell characters (presence of basal band, presence of basal ridge, and size of checker pattern) as well as tentacle coloration. The four discrete characters differ significantly between the two species, though none is completely diagnostic. Tentacle coloration is the most reliable character and may be combined with the shell characters for successful identification. The two species also differ significantly in overall size and in three out of five size-independent shell shape measurements, with L scunilata having larger, taller-spired shells with narrower apertures. However, shell shape does not separate the species well because of intraspecific variation, and it is unlikely to be useful for species identification. Further analysis suggests that at least some of this intraspecific variation is genetic rather than environmental. The distributions of the two species overlap broadly in Washington, though only L plena was found in exposed outer coast habilals, contrary to previous work.

The vulnerability of burrowing bivalves to shell-breaking predation by crabs was found to be infl... more The vulnerability of burrowing bivalves to shell-breaking predation by crabs was found to be influenced strongly by shell features: size, shell thickness, degree of inflation, and the presence or absence of a gape.

ABSTRACT Thesis (Ph. D.)--University of Washington, 1990 A new species Littorina tatooshensis fro... more ABSTRACT Thesis (Ph. D.)--University of Washington, 1990 A new species Littorina tatooshensis from the Northeastern Pacific is described on the basis of morphological and behavioural differences, hybridization studies, and allozyme electrophoresis. Genetic differences in shell morphology were identified among (1) the new species L. tatooshensis, (2) Littorina sitkana which occurs in contiguous habitats in the Northeastern Pacific, and (3) Littorina kurila from further west in the Northern Pacific, by culturing them in a common environment. There was considerable morphological overlap among the three species. L. tatooshensis cultured at low density had faster growth rates, higher spires, and narrower apertures than their siblings cultured at high density; but L. sitkana cultured at low density had the same shape as L. sitkana grown more slowly in the field but were smooth rather than heavily ridged.L. tatooshensis was found only on wave-exposed shores and survived poorly when transplanted to protected shores containing predatory crabs. The larger, thick-shelled, protected shore species, L. sitkana, survived moderately well when transplanted onto exposed shores but would be unlikely to reach maturity before being washed away in winter storms.Heritabilities of some shell form traits were estimated for a L. tatooshensis population in order to predict the short term response to selection on these traits. Quantitative genetic analysis was done using a half-sib design with each brood of full sibs split between two environments. Significant heritability estimates were obtained for shell size and shape and for aperture shape. Significant genetic correlations were obtained between shell shape parameters. Such correlations can constrain the response of a trait to directional selection unless selection is strong.A simulation model was constructed for a polygenic, quantitative trait that experiences different selective pressures on exposed and sheltered shores; genetic differences were maintained between the two populations despite high intermigration rates even though the model did not include mutation. Changing the phenotypic plasticity from random to adaptive reduced the ability of selection to maintain genetic differentiation between the two populations. Genetic differences between exposed and protected populations can persist for significant periods of time and may have sometimes been the first step in speciation.

Animals living in intertidal habitats experience high temperatures and low humidity during emersi... more Animals living in intertidal habitats experience high temperatures and low humidity during emersion that represent extreme deviations from those experienced during immersion; some use behaviour to ameliorate these stressors. We made in situ observations of 3 behaviours displayed by the Pacific intertidal snail Littorina subrotundata on 3 exposed rocky intertidal shores in the northeast Pacific: microhabitat selection, activity level, and conspecific aggregation. We hypothesized that these behaviours might be altered in response to temperature and/or humidity at a particular time during tidal emersion. We used the Akaike information criterion to compare a set of models for each of the 3 behaviours that included combinations of substrate temperature (T s ), vapour pressure deficit (VPD) (which encompasses humidity), emersion time, snail shell width (Size), and study site (Site) as the independent variables. The best supported model of microhabitat selection in the summers of 2011 and 2012 used only the independent variables Site and Size. The best supported model of activity included both T s and VPD in 2011 but included only T s in 2012; increased T s resulted in decreased activity. None of the models in the set explained much of the variance in conspecific aggregation. We conclude an alternate cue for microhabitat selection is likely in this system and suggest that biogenic refuges created by barnacles are a likely driver. Our findings also suggest that thermal stress during emersion is the primary cue that informs the snails to reduce their activity.

Comparative genome scans can be used to identify chromosome regions, but not traits, that are put... more Comparative genome scans can be used to identify chromosome regions, but not
traits, that are putatively under selection. Identification of targeted traits may be more
likely in recently domesticated populations under strong artificial selection for
increased production. We used a North American Atlantic salmon 6K SNP dataset to
locate genome regions of an aquaculture strain (Saint John River) that were highly
diverged from that of its putative wild founder population (Tobique River). First,
admixed individuals with partial European ancestry were detected using STRUCTURE
and removed from the dataset. Outlier loci were then identified as those showing
extreme differentiation between the aquaculture population and the founder
population. All Arlequin methods identified an overlapping subset of 17 outlier loci,
three of which were also identified by BayeScan. Many outlier loci were near candidate
genes and some were near published quantitative trait loci (QTLs) for growth, appetite,
maturity, or disease resistance. Parallel comparisons using a wild, nonfounder
population (Stewiacke River) yielded only one overlapping outlier locus as well as a
known maturity QTL. We conclude that genome scans comparing a recently
domesticated strain with its wild founder population can facilitate identification of
candidate genes for traits known to have been under strong artificial selection

The intertidal snail Littorina saxatilis has repeatedly evolved two parallel ecotypes assumed to ... more The intertidal snail Littorina saxatilis has repeatedly evolved two parallel ecotypes assumed to be wave adapted and predatory shore crab adapted, but the magnitude and targets of predator-driven selection are unknown. In Spain, a small, wave ecotype with a large aperture from the lower shore and a large, thick-shelled crab ecotype from the upper shore meet in the mid-shore and show partial size-assortative mating. We performed complementary field tethering and laboratory predation experiments; the first set compared the survival of two different size-classes of the crab ecotype while the second compared the same size-class of the two ecotypes. In the first set, the large size-class of the crab ecotype survived significantly better than the small size-class both on the upper shore and in the laboratory. In the second set, the small size-class of the crab ecotype survived substantially better than that of the wave ecotype both on the upper shore and in the laboratory. Shell-breaking predation on tethered snails was almost absent within the lower shore. In the laboratory shore crabs (Pachygrapsus marmoratus) with larger claw heights selected most strongly against the small sizeclass of the crab ecotype, whereas those with medium claw heights selected most strongly against the thin-shelled wave ecotype. Sexual maturity occurred at a much larger size in the crab ecotype than in the wave ecotype. Our results showed that selection on the upper shore for rapid attainment of a size refuge from this gape-limited predator favors large size, thick shells, and late maturity. Model parameterization showed that size-selective predation restricted to the upper shore resulted in the evolution of the crab ecotype despite gene flow from the wave ecotype snails living on the lower shore. These results on gape-limited predation and previous ones showing size-assortative mating between ecotypes suggest that size may represent a magic trait for the thick-shelled ecotype.

Oceanography and Marine Biology - An Annual Review, 2015

Journal of Molluscan Studies, 2015

Journal of Evolutionary Biology, 2007

Prey populations after a predator invasion 1987 ª 2 0 0 7 T H E A U T H O R S . J . E V O L . B I... more Prey populations after a predator invasion 1987 ª 2 0 0 7 T H E A U T H O R S . J . E V O L . B I O L . 2 0 ( 2 0 0 7 ) 1 9 7 6 -1 9 8 7 J O U R N A L C O M P I L A T I O N ª 2 0 0 7 E U R O P E

BMC Genomics, 2012

Background: Geographical isolation has generated a distinct difference between Atlantic salmon of... more Background: Geographical isolation has generated a distinct difference between Atlantic salmon of European and North American Atlantic origin. The European Atlantic salmon generally has 29 pairs of chromosomes and 74 chromosome arms whereas it has been reported that the North American Atlantic salmon has 27 chromosome pairs and an NF of 72. In order to predict the major chromosomal rearrangements causing these differences, we constructed a dense linkage map for Atlantic salmon of North American origin and compared it with the well-developed map for European Atlantic salmon. Results: The presented male and female genetic maps for the North American subspecies of Atlantic salmon, contains 3,662 SNPs located on 27 linkage groups. The total lengths of the female and male linkage maps were 2,153 cM and 968 cM respectively, with males characteristically showing recombination only at the telomeres. We compared these maps with recently published SNP maps from European Atlantic salmon, and predicted three chromosomal reorganization events that we then tested using fluorescence in situ hybridization (FISH) analysis. The proposed rearrangements, which define the differences in the karyotypes of the North American Atlantic salmon relative to the European Atlantic salmon, include the translocation of the p arm of ssa01 to ssa23 and polymorphic fusions: ssa26 with ssa28, and ssa08 with ssa29.

Journal of Evolutionary Biology, 2010

Hydrobiologia, 1998

We investigated whether measurements of barnacle microtopography could be used as covariates to i... more We investigated whether measurements of barnacle microtopography could be used as covariates to increase precision in randomised field experiments with intertidal Littorina populations. We used image analysis to quantify the microtopography of the barnacles within 100 cm 2 quadrats in July 1994 using as variables: number of barnacles, number of dead empty barnacles, mean distance to nearest neighbouring barnacle, total area covered by barnacles, and number of pockets of different size-classes [extra-small (< 0.15 cm 2 ), small (≥ 0.15 and < 0.30 cm 2 ), medium (≥ 0.30 and < 0.45 cm 2 ), large (≥ 0.45 and < 0.60 cm 2 ), and extra-large (≥ 0.60 cm 2 )] at least 75% surrounded by barnacles. We then used these variables to predict the abundance of Littorina spp. in the same quadrat. Two variables: the number of extra-small pockets and the number of small pockets accounted for 50% of the variation in total littorinid snail abundance among quadrats for January 1995 and for 47% of the variation for August 1994 but for only 16% of the variation for June 1994. However the single variable, the number of barnacles, accounted for 29-36% of the variation in snail abundance on these dates and can be measured without special equipment. The best combination of covariates was the number of extra-small pockets alone. The number of extra-small pockets between barnacles may be influencing the snail abundance by providing a refuge from wave shock and heat stress/desiccation. We suggest that the availability of these refuges among the barnacles could act as a density-dependent regulator of the total population size of a particular species of Littorina.

Integrative and Comparative Biology, Jan 1, 2010

BMC Genomics, Aug 28, 2012

Background: Geographical isolation has generated a distinct difference between Atlantic salmon of... more Background: Geographical isolation has generated a distinct difference between Atlantic salmon of European and North American Atlantic origin. The European Atlantic salmon generally has 29 pairs of chromosomes and 74 chromosome arms whereas it has been reported that the North American Atlantic salmon has 27 chromosome pairs and an NF of 72. In order to predict the major chromosomal rearrangements causing these differences, we constructed a dense linkage map for Atlantic salmon of North American origin and compared it with the well-developed map for European Atlantic salmon. Results: The presented male and female genetic maps for the North American subspecies of Atlantic salmon, contains 3,662 SNPs located on 27 linkage groups. The total lengths of the female and male linkage maps were 2,153 cM and 968 cM respectively, with males characteristically showing recombination only at the telomeres. We compared these maps with recently published SNP maps from European Atlantic salmon, and predicted three chromosomal reorganization events that we then tested using fluorescence in situ hybridization (FISH) analysis. The proposed rearrangements, which define the differences in the karyotypes of the North American Atlantic salmon relative to the European Atlantic salmon, include the translocation of the p arm of ssa01 to ssa23 and polymorphic fusions: ssa26 with ssa28, and ssa08 with ssa29.

Journal of …, Jan 1, 2001

The pile perch, Rhacnchilus vacea (Embiotocidae). is abundant on the Pacific Coast of North Ameii... more The pile perch, Rhacnchilus vacea (Embiotocidae). is abundant on the Pacific Coast of North Ameiica and is known to crush hard-shelled prey with its heavy pharyngeal teeth. We investigated whether pile perch predation has the potential to limit or regulate populations of Littorina .<iitkana, a direct-developing gastropod found on wave-sheltered shores near Bamfield, British Columbia. Canada. Laboratory experiments showed that pile perch required an average of only 19.2 sec (SE = 5.61: « = 20) to crush and swallow a large L. silkami. which resulted in consumption rates averaging 33.3 (SE = 6.27; n = 4) large snails per day. The snails had no size refuge from predation by adult fish because even small fish (fork length 21 cm) could crush the largest L sitkana present on the shore (>1 1 mm shell width). Indeed, some fish showed a significant preference for large snails {shell width >6.3 mm) over small snails (3.35 mm < shell width < 4.0 mm). Our 1998 observations with SCUBA during daytime high tides showed that the density of pile perch foraging in the intertidal averaged 0.1 19 (SE = 0.0205; n = 20) individuals per square meter (estimated fork lengths 5^0 cm). However, the intertidal distribution of pile perch that were actually consuming prey was highly aggregated. In the field, we investigated whether predation by this fish on snails deployed onto boulders was density dependent. The fish swam parallel to the shore and located and consumed 4()'/f of the patches of L. siikiiiui that we deployed (;? = 70) within 50 min. This foraging behavior resulted in density-dependent predation on the deployed snails in only one of the three tidal cycles (or 2 of the 12 days) of our experiment. We offer several proximate reasons for the low frequency of density-dependent predation found in this study and conclude that the pile perch may not be an important regulating factor for L. siikiiiui populations at this site at the present time. However, the very high predation rates we observed suggest that this predatory fish is an important limiting factor at this site.

Conservation Genetics, Jan 1, 2012

Journal of …, Jan 1, 2001

Sibling specie.s Litwrina sculidciui and L. plena are difficult to distinguish in the field. Here... more Sibling specie.s Litwrina sculidciui and L. plena are difficult to distinguish in the field. Here we present a new molecular liiul and use it lo evaluate the discrete and quantitative morphological characters that have been proposed as diagnostic. We collected 38.5 snails of both species from 1 1 sites in Washington state and used restriction enzyme digestion of a PCR-amplified, 480 bp fragment of the mitochondrial cytochrome b gene to distinguish the species. This new molecular assay produces species-specific restriction fragment patterns that correspond with identification of males by penis morphology. To evaluate the usefulness of morphological characters, we scored three discrete shell characters (presence of basal band, presence of basal ridge, and size of checker pattern) as well as tentacle coloration. The four discrete characters differ significantly between the two species, though none is completely diagnostic. Tentacle coloration is the most reliable character and may be combined with the shell characters for successful identification. The two species also differ significantly in overall size and in three out of five size-independent shell shape measurements, with L scunilata having larger, taller-spired shells with narrower apertures. However, shell shape does not separate the species well because of intraspecific variation, and it is unlikely to be useful for species identification. Further analysis suggests that at least some of this intraspecific variation is genetic rather than environmental. The distributions of the two species overlap broadly in Washington, though only L plena was found in exposed outer coast habilals, contrary to previous work.

The vulnerability of burrowing bivalves to shell-breaking predation by crabs was found to be infl... more The vulnerability of burrowing bivalves to shell-breaking predation by crabs was found to be influenced strongly by shell features: size, shell thickness, degree of inflation, and the presence or absence of a gape.

ABSTRACT Thesis (Ph. D.)--University of Washington, 1990 A new species Littorina tatooshensis fro... more ABSTRACT Thesis (Ph. D.)--University of Washington, 1990 A new species Littorina tatooshensis from the Northeastern Pacific is described on the basis of morphological and behavioural differences, hybridization studies, and allozyme electrophoresis. Genetic differences in shell morphology were identified among (1) the new species L. tatooshensis, (2) Littorina sitkana which occurs in contiguous habitats in the Northeastern Pacific, and (3) Littorina kurila from further west in the Northern Pacific, by culturing them in a common environment. There was considerable morphological overlap among the three species. L. tatooshensis cultured at low density had faster growth rates, higher spires, and narrower apertures than their siblings cultured at high density; but L. sitkana cultured at low density had the same shape as L. sitkana grown more slowly in the field but were smooth rather than heavily ridged.L. tatooshensis was found only on wave-exposed shores and survived poorly when transplanted to protected shores containing predatory crabs. The larger, thick-shelled, protected shore species, L. sitkana, survived moderately well when transplanted onto exposed shores but would be unlikely to reach maturity before being washed away in winter storms.Heritabilities of some shell form traits were estimated for a L. tatooshensis population in order to predict the short term response to selection on these traits. Quantitative genetic analysis was done using a half-sib design with each brood of full sibs split between two environments. Significant heritability estimates were obtained for shell size and shape and for aperture shape. Significant genetic correlations were obtained between shell shape parameters. Such correlations can constrain the response of a trait to directional selection unless selection is strong.A simulation model was constructed for a polygenic, quantitative trait that experiences different selective pressures on exposed and sheltered shores; genetic differences were maintained between the two populations despite high intermigration rates even though the model did not include mutation. Changing the phenotypic plasticity from random to adaptive reduced the ability of selection to maintain genetic differentiation between the two populations. Genetic differences between exposed and protected populations can persist for significant periods of time and may have sometimes been the first step in speciation.