Melanie Lancaster | La Trobe University (original) (raw)

Papers by Melanie Lancaster

Research paper thumbnail of Population structure and genetic diversity of the black-footed rock-wallaby (Petrogale lateralis MacDonnell Ranges race)

Australian Journal of Zoology

... and St Elias Range) that presumably would foster greater population differentiation. Genetic ... more ... and St Elias Range) that presumably would foster greater population differentiation. Genetic distances between Alaska populations in close proximity (ie, Seward Peninsula, Koyukuk, and Tanana Flats) were less than a similarly arrayed group of moose populations described ...

Research paper thumbnail of Fur seals at Macquarie Island: post-sealing colonisation, trends in abundance and hybridisation of three species

Polar Biology, 2009

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early... more Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The Wrst breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954-2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is signiWcant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been aVected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.

Research paper thumbnail of Population status and trends in the abundance of the fur seals at Macquarie Island

... Simon D Goldsworthy, Jane McKenzie, Brad Page, Melanie Lancaster, Natalie Bool South Australi... more ... Simon D Goldsworthy, Jane McKenzie, Brad Page, Melanie Lancaster, Natalie Bool South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5481 www.sardi.sa.gov ...

Research paper thumbnail of Fur seals at Macquarie Island: post-sealing colonisation, trends in abundance and hybridisation of three species

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early... more Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The Wrst breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954-2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is signiWcant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been aVected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.

Research paper thumbnail of Australian fur seals establish haulout sites and a breeding colony in South Australia

Australian Journal of Zoology, 2010

Australian fur seals (Arctocephalus pusillus doriferus) breed on Bass Strait islands in Victoria ... more Australian fur seals (Arctocephalus pusillus doriferus) breed on Bass Strait islands in Victoria and Tasmania. They have been recorded in South Australia (SA) for many years as non-breeding visitors and on Kangaroo Island frequently since 1988, mostly in breeding colonies of the New Zealand fur seal (A. forsteri) which is the most numerous pinniped in SA. Australian fur seals have displaced New Zealand fur seals from sections of the Cape Gantheaume colony on Kangaroo Island. North Casuarina Island produced 29 Australian fur seal pups in February 2008. Australian fur seal pups were larger than New Zealand fur seal pups in the same colony and have been identified genetically using a 263-bp fragment of the mitochondrial DNA control region. North Casuarina Island has been an important breeding colony of New Zealand fur seals, but pup numbers there decreased since 1992-93 (contrary to trends in SA for New Zealand fur seals), while numbers of Australian fur seals there have increased. This study confirms that Australian fur seals breed in SA. The two fur seal species compete for space onshore at several sites. Australian fur seals may compete for food with endangered Australian sea lions (Neophoca cinerea) because both are bottom feeders.

Research paper thumbnail of Microsatellite markers for the Common ringtail possum (Pseudocheirus peregrinus) and their amplification in other Pseudocheirids

Molecular ecology resources, 2009

Eleven microsatellite markers were developed for the Common ringtail possum, an arboreal marsupia... more Eleven microsatellite markers were developed for the Common ringtail possum, an arboreal marsupial abundant in fragmented forests of south-eastern Australia. Loci were highly polymorphic (4-32 alleles per locus) and heterozygosity ranged from 0.66 to 1. Two loci deviated significantly from Hardy-Weinberg equilibrium proportions, possibly because of low-frequency null alleles. These markers will be informative for examining patterns of gene flow, relatedness and mating systems within fragmented populations of the Common ringtail possum and have potential for use in other Pseudocheirids.

Research paper thumbnail of Multiple mating strategies explain unexpected genetic mixing of New Zealand fur seals with two congenerics in a recently recolonized population

Molecular Ecology, 2007

Human impacts on natural systems can cause local population extinctions, which may promote redist... more Human impacts on natural systems can cause local population extinctions, which may promote redistribution of taxa and secondary contact between divergent lineages. In mammalian populations that have mating systems shaped by polygyny and sexual selection, the potential for hybridization to ensue and persist depends on individual and demographic factors. At Macquarie Island, a recently formed fur seal population is comprised of both sexes of breeding Antarctic (Arctocephalus gazella) and subantarctic (A. tropicalis) fur seals, and an itinerant collection of male New Zealand fur seals (A. forsteri), presumed to be non-breeders due to their absence from principle breeding areas. The mating system of the three species is described as resource-defence polygyny: males defend beach territories containing breeding females for exclusive mating rights. A recent genetic study identified a high level of hybridization in the population (17-30%), unexpectedly involving all three species. This study examined the source of involvement in breeding by A. forsteri with respect to mating strategies operating in the population. Ninety-five (10%) pups born from 1992 to 2003 were genetically identified as New Zealand hybrids. Most resulted from reproduction within territories by New Zealand hybrids of both sexes, although some were conceived extraterritorially, indicating that males successfully utilize strategies other than territory holding to achieve paternities. Female reproductive status influenced mating partner and mating location, and females without pups were more likely to conceive extra-territorially and with A. forsteri males. This study illustrates an important consequence of low heterospecific discrimination in a sympatric population of long-lived mammals.

Research paper thumbnail of Population status and trends in the abundance of the fur seals at Macquarie Island

... Simon D Goldsworthy, Jane McKenzie, Brad Page, Melanie Lancaster, Natalie Bool South Australi... more ... Simon D Goldsworthy, Jane McKenzie, Brad Page, Melanie Lancaster, Natalie Bool South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5481 www.sardi.sa.gov ...

Research paper thumbnail of Fur seals at Macquarie Island: post-sealing colonisation, trends in abundance and hybridisation of three species

Polar Biology, 2009

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early... more Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The Wrst breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954-2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is signiWcant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been aVected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.

Research paper thumbnail of Lower reproductive success in hybrid fur seal males indicates fitness costs to hybridization

Hybridization among organisms can potentially contribute to the processes of evolution, but this ... more Hybridization among organisms can potentially contribute to the processes of evolution, but this depends on the fitness of hybrids relative to parental species. A small, recently formed population of fur seals on subantarctic Macquarie Island contains a high proportion of hybrids (17-30%) derived from combinations of three parental species: Antarctic, subantarctic and New Zealand fur seals. Mitochondrial control-region data (restriction fragment length polymorphisms) and nine microsatellites were used to determine the species composition of breeding adults, and hybrid male fitness was measured by comparing reproductive success (number of genetically inferred paternities) of hybrid and pure-species territory males over 6 years. No correlations were found between male reproductive success and three genetic measures of outbreeding, but this may be due to a relatively small number of dominant males analysed. Territory males fathered 63% of pups, but hybrid males had lower reproductive success than pure-species males despite having the same ability to hold territories. A greater proportion of females in hybrid male territories conceived extra-territorially than those in territories of pure-species males, and most (70 of 82) mated with conspecifics. This suggests the presence of reproductive isolating mechanisms that promote positive assortative mating and reduce the production of hybrid offspring. Although we found no evidence for male sterility in the population, mechanisms that reduce lifetime reproductive success may act to decrease the frequency of hybrids. Our study has identified a disadvantage of hybridization -reduced reproductive success of hybrid sons -that may be contributing to the persistence of pure lineages at Macquarie Island and the temporal decline in hybridization observed there.

Research paper thumbnail of Single copy nuclear DNA markers for the onychophoran Phallocephale tallagandensis

Conservation Genetics Resources, 2009

For some species, particularly invertebrates, developing single copy nuclear markers is an expens... more For some species, particularly invertebrates, developing single copy nuclear markers is an expensive and time-consuming task that may result in few or no usable markers. This has proven true for Onychophora (velvet worms). Here we describe our PCR-based method of generating single copy nuclear markers in Onychophora-a phylum comprised of species generally regarded as rare and of high conservation value-for which suitable microsatellites have been difficult to obtain. We list 6 primer pairs, some of which amplify across genera, and demonstrate their utility in identifying strong population structure in the species Phallocephale tallagandensis.

Research paper thumbnail of Two behavioural traits promote fine-scale species segregation and moderate hybridisation in a recovering sympatric fur seal population

BMC Evolutionary Biology

Background: In systems where two or more species experience secondary contact, behavioural factor... more Background: In systems where two or more species experience secondary contact, behavioural factors that regulate interspecific gene flow may be important for maintaining species boundaries and reducing the incidence of hybridisation. At subantarctic Macquarie Island, two species of fur seal breed in close proximity to one another, hybridise at very high levels (up to 21% of hybrid pups are born annually), yet retain discrete gene pools. Using spatial and genetic information collected for pups and adults over twelve years, we assessed two behavioural traits -interannual site fidelity and differences in habitat use between the species -as possible contributors to the maintenance of this species segregation. Further, we explored the breakdown of these traits in pure-species individuals and hybrids.

Research paper thumbnail of Environmentally related patterns of reproductive modes in the aphid Myzus persicae and the predominance of two 'superclones' in Victoria, Australia

Molecular Ecology, 2003

Asexual organisms that naturally coexist with sexual relatives may hold the key to understanding ... more Asexual organisms that naturally coexist with sexual relatives may hold the key to understanding the maintenance of sex and recombination, a long-standing problem in evolutionary biology. This situation applies to the peach-potato aphid, Myzus persicae , in southeastern Australia where cyclical parthenogens form mixed populations with obligate parthenogens. We collected M. persicae from several areas across Victoria, genotyped them at seven microsatellite loci and experimentally determined their reproductive mode. The geographic distribution of reproductive modes was correlated with two environmental variables that differentially affect obligate and cyclical parthenogens; obligate parthenogens were less frequent in areas with cold winters because they cannot produce frost-resistant eggs while cyclical parthenogens were limited by the availability of their primary host, peach, on which sexual reproduction takes place. Clonal diversity increased with the proportion of cyclical parthenogens in a sample because they tended to have unique microsatellite genotypes, whereas many obligate parthenogens were copies of the same genotype. Two obligately asexual genotypes stood out as being very abundant and widespread, one constituting 24% and the other 17.4% of the entire collection. Both of these highly successful genotypes were present in the majority of all collection sites. Genetic population structure was weak, albeit significant, with a multilocus F ST of only 0.021 when samples were reduced to only one representative of each genotype. Interestingly, obligate parthenogens were, on average, more heterozygous and exhibited larger allele size differences between the two alleles at individual loci than cyclical parthenogens. This striking pattern could result from hybridization, for which we have no evidence, or may reflect the previously proposed model of biased mutational divergence of microsatellite alleles within asexual aphid lineages.

Research paper thumbnail of Population structure and genetic diversity of the black-footed rock-wallaby (Petrogale lateralis MacDonnell Ranges race)

Australian Journal of Zoology

... and St Elias Range) that presumably would foster greater population differentiation. Genetic ... more ... and St Elias Range) that presumably would foster greater population differentiation. Genetic distances between Alaska populations in close proximity (ie, Seward Peninsula, Koyukuk, and Tanana Flats) were less than a similarly arrayed group of moose populations described ...

Research paper thumbnail of Fur seals at Macquarie Island: post-sealing colonisation, trends in abundance and hybridisation of three species

Polar Biology, 2009

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early... more Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The Wrst breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954-2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is signiWcant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been aVected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.

Research paper thumbnail of Population status and trends in the abundance of the fur seals at Macquarie Island

... Simon D Goldsworthy, Jane McKenzie, Brad Page, Melanie Lancaster, Natalie Bool South Australi... more ... Simon D Goldsworthy, Jane McKenzie, Brad Page, Melanie Lancaster, Natalie Bool South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5481 www.sardi.sa.gov ...

Research paper thumbnail of Fur seals at Macquarie Island: post-sealing colonisation, trends in abundance and hybridisation of three species

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early... more Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The Wrst breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954-2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is signiWcant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been aVected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.

Research paper thumbnail of Australian fur seals establish haulout sites and a breeding colony in South Australia

Australian Journal of Zoology, 2010

Australian fur seals (Arctocephalus pusillus doriferus) breed on Bass Strait islands in Victoria ... more Australian fur seals (Arctocephalus pusillus doriferus) breed on Bass Strait islands in Victoria and Tasmania. They have been recorded in South Australia (SA) for many years as non-breeding visitors and on Kangaroo Island frequently since 1988, mostly in breeding colonies of the New Zealand fur seal (A. forsteri) which is the most numerous pinniped in SA. Australian fur seals have displaced New Zealand fur seals from sections of the Cape Gantheaume colony on Kangaroo Island. North Casuarina Island produced 29 Australian fur seal pups in February 2008. Australian fur seal pups were larger than New Zealand fur seal pups in the same colony and have been identified genetically using a 263-bp fragment of the mitochondrial DNA control region. North Casuarina Island has been an important breeding colony of New Zealand fur seals, but pup numbers there decreased since 1992-93 (contrary to trends in SA for New Zealand fur seals), while numbers of Australian fur seals there have increased. This study confirms that Australian fur seals breed in SA. The two fur seal species compete for space onshore at several sites. Australian fur seals may compete for food with endangered Australian sea lions (Neophoca cinerea) because both are bottom feeders.

Research paper thumbnail of Microsatellite markers for the Common ringtail possum (Pseudocheirus peregrinus) and their amplification in other Pseudocheirids

Molecular ecology resources, 2009

Eleven microsatellite markers were developed for the Common ringtail possum, an arboreal marsupia... more Eleven microsatellite markers were developed for the Common ringtail possum, an arboreal marsupial abundant in fragmented forests of south-eastern Australia. Loci were highly polymorphic (4-32 alleles per locus) and heterozygosity ranged from 0.66 to 1. Two loci deviated significantly from Hardy-Weinberg equilibrium proportions, possibly because of low-frequency null alleles. These markers will be informative for examining patterns of gene flow, relatedness and mating systems within fragmented populations of the Common ringtail possum and have potential for use in other Pseudocheirids.

Research paper thumbnail of Multiple mating strategies explain unexpected genetic mixing of New Zealand fur seals with two congenerics in a recently recolonized population

Molecular Ecology, 2007

Human impacts on natural systems can cause local population extinctions, which may promote redist... more Human impacts on natural systems can cause local population extinctions, which may promote redistribution of taxa and secondary contact between divergent lineages. In mammalian populations that have mating systems shaped by polygyny and sexual selection, the potential for hybridization to ensue and persist depends on individual and demographic factors. At Macquarie Island, a recently formed fur seal population is comprised of both sexes of breeding Antarctic (Arctocephalus gazella) and subantarctic (A. tropicalis) fur seals, and an itinerant collection of male New Zealand fur seals (A. forsteri), presumed to be non-breeders due to their absence from principle breeding areas. The mating system of the three species is described as resource-defence polygyny: males defend beach territories containing breeding females for exclusive mating rights. A recent genetic study identified a high level of hybridization in the population (17-30%), unexpectedly involving all three species. This study examined the source of involvement in breeding by A. forsteri with respect to mating strategies operating in the population. Ninety-five (10%) pups born from 1992 to 2003 were genetically identified as New Zealand hybrids. Most resulted from reproduction within territories by New Zealand hybrids of both sexes, although some were conceived extraterritorially, indicating that males successfully utilize strategies other than territory holding to achieve paternities. Female reproductive status influenced mating partner and mating location, and females without pups were more likely to conceive extra-territorially and with A. forsteri males. This study illustrates an important consequence of low heterospecific discrimination in a sympatric population of long-lived mammals.

Research paper thumbnail of Population status and trends in the abundance of the fur seals at Macquarie Island

... Simon D Goldsworthy, Jane McKenzie, Brad Page, Melanie Lancaster, Natalie Bool South Australi... more ... Simon D Goldsworthy, Jane McKenzie, Brad Page, Melanie Lancaster, Natalie Bool South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5481 www.sardi.sa.gov ...

Research paper thumbnail of Fur seals at Macquarie Island: post-sealing colonisation, trends in abundance and hybridisation of three species

Polar Biology, 2009

Commercial sealers exterminated the original fur seal population at Macquarie Island in the early... more Commercial sealers exterminated the original fur seal population at Macquarie Island in the early 1800s. The Wrst breeding record since the sealing era was not reported until March 1955. Three species of fur seal now occur at Macquarie Island, the Antarctic (Arctocephalus gazella), subantarctic (A. tropicalis) and New Zealand (A. forsteri) fur seal. Census data from 54 breeding seasons in the period 1954-2007 were used to estimate population status and growth for each species. Between the 1950s and 1970s, annual increases in pup production for the species aggregate were low. Between 1986 and 2007, pup production of Antarctic fur seals increased by about 8.8% per year and subantarctic fur seals by 6.8% per year. The New Zealand fur seal, although the most numerous fur seal species on Macquarie Island, has yet to establish a breeding population, due to the absence of reproductively mature females. Hybridisation among species is signiWcant, but appears to be declining. The slow establishment and growth of fur seal populations on Macquarie Island appears to have been aVected by its distance from major population centres and hence low immigration rates, asynchronous colonisation times of males and females of each species, and extensive hybridisation.

Research paper thumbnail of Lower reproductive success in hybrid fur seal males indicates fitness costs to hybridization

Hybridization among organisms can potentially contribute to the processes of evolution, but this ... more Hybridization among organisms can potentially contribute to the processes of evolution, but this depends on the fitness of hybrids relative to parental species. A small, recently formed population of fur seals on subantarctic Macquarie Island contains a high proportion of hybrids (17-30%) derived from combinations of three parental species: Antarctic, subantarctic and New Zealand fur seals. Mitochondrial control-region data (restriction fragment length polymorphisms) and nine microsatellites were used to determine the species composition of breeding adults, and hybrid male fitness was measured by comparing reproductive success (number of genetically inferred paternities) of hybrid and pure-species territory males over 6 years. No correlations were found between male reproductive success and three genetic measures of outbreeding, but this may be due to a relatively small number of dominant males analysed. Territory males fathered 63% of pups, but hybrid males had lower reproductive success than pure-species males despite having the same ability to hold territories. A greater proportion of females in hybrid male territories conceived extra-territorially than those in territories of pure-species males, and most (70 of 82) mated with conspecifics. This suggests the presence of reproductive isolating mechanisms that promote positive assortative mating and reduce the production of hybrid offspring. Although we found no evidence for male sterility in the population, mechanisms that reduce lifetime reproductive success may act to decrease the frequency of hybrids. Our study has identified a disadvantage of hybridization -reduced reproductive success of hybrid sons -that may be contributing to the persistence of pure lineages at Macquarie Island and the temporal decline in hybridization observed there.

Research paper thumbnail of Single copy nuclear DNA markers for the onychophoran Phallocephale tallagandensis

Conservation Genetics Resources, 2009

For some species, particularly invertebrates, developing single copy nuclear markers is an expens... more For some species, particularly invertebrates, developing single copy nuclear markers is an expensive and time-consuming task that may result in few or no usable markers. This has proven true for Onychophora (velvet worms). Here we describe our PCR-based method of generating single copy nuclear markers in Onychophora-a phylum comprised of species generally regarded as rare and of high conservation value-for which suitable microsatellites have been difficult to obtain. We list 6 primer pairs, some of which amplify across genera, and demonstrate their utility in identifying strong population structure in the species Phallocephale tallagandensis.

Research paper thumbnail of Two behavioural traits promote fine-scale species segregation and moderate hybridisation in a recovering sympatric fur seal population

BMC Evolutionary Biology

Background: In systems where two or more species experience secondary contact, behavioural factor... more Background: In systems where two or more species experience secondary contact, behavioural factors that regulate interspecific gene flow may be important for maintaining species boundaries and reducing the incidence of hybridisation. At subantarctic Macquarie Island, two species of fur seal breed in close proximity to one another, hybridise at very high levels (up to 21% of hybrid pups are born annually), yet retain discrete gene pools. Using spatial and genetic information collected for pups and adults over twelve years, we assessed two behavioural traits -interannual site fidelity and differences in habitat use between the species -as possible contributors to the maintenance of this species segregation. Further, we explored the breakdown of these traits in pure-species individuals and hybrids.

Research paper thumbnail of Environmentally related patterns of reproductive modes in the aphid Myzus persicae and the predominance of two 'superclones' in Victoria, Australia

Molecular Ecology, 2003

Asexual organisms that naturally coexist with sexual relatives may hold the key to understanding ... more Asexual organisms that naturally coexist with sexual relatives may hold the key to understanding the maintenance of sex and recombination, a long-standing problem in evolutionary biology. This situation applies to the peach-potato aphid, Myzus persicae , in southeastern Australia where cyclical parthenogens form mixed populations with obligate parthenogens. We collected M. persicae from several areas across Victoria, genotyped them at seven microsatellite loci and experimentally determined their reproductive mode. The geographic distribution of reproductive modes was correlated with two environmental variables that differentially affect obligate and cyclical parthenogens; obligate parthenogens were less frequent in areas with cold winters because they cannot produce frost-resistant eggs while cyclical parthenogens were limited by the availability of their primary host, peach, on which sexual reproduction takes place. Clonal diversity increased with the proportion of cyclical parthenogens in a sample because they tended to have unique microsatellite genotypes, whereas many obligate parthenogens were copies of the same genotype. Two obligately asexual genotypes stood out as being very abundant and widespread, one constituting 24% and the other 17.4% of the entire collection. Both of these highly successful genotypes were present in the majority of all collection sites. Genetic population structure was weak, albeit significant, with a multilocus F ST of only 0.021 when samples were reduced to only one representative of each genotype. Interestingly, obligate parthenogens were, on average, more heterozygous and exhibited larger allele size differences between the two alleles at individual loci than cyclical parthenogens. This striking pattern could result from hybridization, for which we have no evidence, or may reflect the previously proposed model of biased mutational divergence of microsatellite alleles within asexual aphid lineages.