Gábor Herczeg - Academia.edu (original) (raw)

Papers by Gábor Herczeg

Proceedings of the Royal Society B: Biological Sciences, 2015

The mosaic model of brain evolution postulates that different brain regions are relatively free t... more The mosaic model of brain evolution postulates that different brain regions are relatively free to evolve independently from each other. Such independent evolution is possible only if genetic correlations among the different brain regions are less than unity. We estimated heritabilities, evolvabilities and genetic correlations of relative size of the brain, and its different regions in the three-spined stickleback (Gasterosteus aculeatus). We found that heritabilities were low (average h(2) = 0.24), suggesting a large plastic component to brain architecture. However, evolvabilities of different brain parts were moderate, suggesting the presence of additive genetic variance to sustain a response to selection in the long term. Genetic correlations among different brain regions were low (average rG = 0.40) and significantly less than unity. These results, along with those from analyses of phenotypic and genetic integration, indicate a high degree of independence between different brain regions, suggesting that responses to selection are unlikely to be severely constrained by genetic and phenotypic correlations. Hence, the results give strong support for the mosaic model of brain evolution. However, the genetic correlation between brain and body size was high (rG = 0.89), suggesting a constraint for independent evolution of brain and body size in sticklebacks.

The transition from marine to freshwater life in the threespine stickleback (Gasterosteus aculeat... more The transition from marine to freshwater life in the threespine stickleback (Gasterosteus aculeatus) is accompanied by complex morphological changes-including reduction in bony armor and change in body shape-but experimental evidence for the selective agents behind these evolutionary transitions is sparse. We investigated whether selection by predatory fish affects threespine stickleback morphology differentially when refuge is absent (pelagic lifestyle-ancestral condition) or present (benthic lifestyle-derived condition). Our results show that selection favors low numbers of lateral plates in habitats with refuge, whereas fully plated individuals have a selective advantage in habitats without refuge. We also found that a decrease in the length of the caudal peduncle increased survival probability, irrespective of habitat. The effect of spine lengths on survival was evident only in a multivariate analysis of selection, implying that it is essential to account for phenotypic and genetic correlations between traits before drawing conclusions about the effects of selection on single traits. Apart from uncovering targets and patterns of predator-induced selection on threespine stickleback morphology, our results provide direct evidence to support the hypothesis that differences in antipredator strategies in pelagic versus benthic sticklebacks could play a role in the repeated, independent cases of plate number reduction following freshwater colonization in this species.

Background: Most evolutionary studies on the size of brains and different parts of the brain have... more Background: Most evolutionary studies on the size of brains and different parts of the brain have relied on interspecific comparisons, and have uncovered correlations between brain architecture and various ecological, behavioural and life-history traits. Yet, similar intraspecific studies are rare, despite the fact that they could better determine how selection and phenotypic plasticity influence brain architecture. We investigated the variation in brain size and structure in wild-caught nine-spined sticklebacks (Pungitius pungitius) from eight populations, representing marine, lake, and pond habitats, and compared them to data from a previous common garden study from a smaller number of populations.

BMC Research Notes, 2011

Background Sex-specific DNA markers can serve as tools for molecular sex identification, as well... more Background Sex-specific DNA markers can serve as tools for molecular sex identification, as well as for population genetic inferences. We investigated the potential utility of a microsatellite marker located on sex chromosomes for molecular sexing of Fennoscandian nine-spined sticklebacks (Pungitius pungitius). In addition, we assessed the patterns of allelic differentiation between X and Y chromosomes across the populations to examine if

Amphibia-reptilia, 2009

The conspicuous blue nuptial colouration of Moor Frog (Rana arvalis) males has been associated wi... more The conspicuous blue nuptial colouration of Moor Frog (Rana arvalis) males has been associated with sexual selection; it may provide females with information about benefits to be gained through mate choice. Here we investigated the phenotype-linked fertility hypothesis suggesting that exaggerated traits may advertise fertilization ability. We evaluated conspicuousness of males' colouration and related this to the number of sperm stored in their testes. Contrary to our expectation, we did not find a positive relationship between blueness of males and the number of sperm stored in the testes. We discuss this result in the light of alternative traits that may be advertised by colouration, such as sperm quality or good genes for offspring survival. We now need direct studies of female mate choice and the physiology of the blue nuptial colouration to clarify the evolutionary background of the striking temporal sexual dichromatism in the Moor Frog.

PLOS One, 2012

The estimation of individual fitness and quality are important elements of evolutionary ecologica... more The estimation of individual fitness and quality are important elements of evolutionary ecological research. Over the past six decades, there has been great interest in using fluctuating asymmetry (FA) to represent individual quality, yet, serious technical problems have hampered efforts to estimate the heritability of FA, which, in turn, has limited progress in the investigation of FA from an evolutionary

Ecography, 2009

The ability to store energy is an important life history trait for organisms facing long periods ... more The ability to store energy is an important life history trait for organisms facing long periods without energy income, and in particular for capital breeders such as temperate zone amphibians, which rely on stored energy during reproduction. However, large scale comparative studies of energy stores in populations with different environmental constraints on energy allocation are scarce. We investigated energy storage patterns in spring (after hibernation and before reproduction) in eight common frog Rana temporaria populations exposed to different environmental conditions along a 1600 km latitudinal gradient across Scandinavia (range of annual activity period is 3Á7 months). Analyses of lean body weight (eviscerated body mass), weight of fat bodies, liver weight, and liver fat content, showed that 1) post-hibernation/prebreeding energy stores increased with increasing latitude in both sexes, 2) males generally had larger energy reserves than females and 3) the difference in energy stores between sexes decreased towards the north. Larger energy reserves towards the north can serve as a buffer against less predictable and/or less benign weather conditions during the short activity period, and may also represent a risk-averse tactic connected with a more pronounced iteroparous life history. In females, the continuous and overlapping vitellogenic activity in the north may also demand more reserves in early spring. The general sexual difference could be a consequence of the fact that, at the time of our sampling, females had already invested their energy into reproduction in the given year (i.e. their eggs were already ovulated), while the males' main reproductive activities (e.g. calling, mate searching, sexual competition) occurred later in the season.

Animal Behaviour, 2009

The main benefit of grouping is reduced predation risk, while the main costs are thought to deriv... more The main benefit of grouping is reduced predation risk, while the main costs are thought to derive from competition and increased frequency of social interactions. While the benefits of grouping are well known, its costs have rarely been studied. We studied growth of nine-spined sticklebacks from two marine (high-predation) and two pond (low-predation) populations by rearing them either individually or in groups from hatching until they reached adult size. We found that living in groups had a strong (up to 14%) negative effect on growth in fish from low-predation populations, despite the lack of constraints originating from resource limitation, predation, reproduction or parasites. Group living had no effect on the growth of fish from high-predation populations. We also studied willingness to shoal: fish from all populations showed strong shoaling behaviour. Our results suggest that the social cost of shoaling can be high, but individuals from high-predation populations seem to have adapted to minimize these costs better than individuals from low-predation populations. Ó

Behavioural processes, 2015

Consistent individual differences within (animal personality) and across (behavioural syndrome) b... more Consistent individual differences within (animal personality) and across (behavioural syndrome) behaviours became well recognized during the past decade. Nevertheless, our knowledge about the evolutionary and developmental mechanisms behind the phenomena is still incomplete. Here, we explored if risk-taking and exploration were consistent and linked to different ecologically relevant traits in wild-caught adult male European green lizards (Lacerta viridis) and in their 2-3 weeks old laboratory-reared offspring. Both adults and juveniles displayed animal personality, consistency being higher in juveniles. We found correlation between risk-taking and exploration (suggestive of a behavioural syndrome) only in adults. Juveniles were more explorative than adults. Large or ectoparasite-free adult males were more explorative than small or parasitized males. Juvenile females tended to be more risk-taking than males. Behaviour of fathers and their offspring did not correlate. We conclude tha...

Ecology and Evolution, 2013

The brain is a trait of central importance for organismal performance and fitness. To date, evolu... more The brain is a trait of central importance for organismal performance and fitness. To date, evolutionary studies of brain size variation have mainly utilized comparative methods applied at the level of species or higher taxa. However, these studies suffer from the difficulty of separating causality from correlation. In the other extreme, studies of brain plasticity have focused mainly on within-population patterns. Between these extremes lie interpopulational studies, focusing on brain size variation among populations of the same species that occupy different habitats or selective regimes. These studies form a rapidly growing field of investigations which can help us to understand brain evolution by providing a test bed for ideas born out of interspecific studies, as well as aid in uncovering the relative importance of genetic and environmental factors shaping variation in brain size and architecture. Aside from providing the first in depth review of published intraspecific studies of brain size variation, we discuss the prospects embedded with interpopulational studies of brain size variation. In particular, the following topics are identified as deserving further attention: (i) studies focusing on disentangling the contributions of genes, environment, and their interactions on brain variation within and among populations, (ii) studies applying quantitative genetic tools to evaluate the relative importance of genetic and environmental factors on brain features at different ontogenetic stages, (iii) apart from utilizing simple gross estimates of brain size, future studies could benefit from use of neuroanatomical, neurohistological, and/or molecular methods in characterizing variation in brain size and architecture.

PLoS ONE, 2011

Background: In spite that chemoreception is important in sexual selection for many animals, such ... more Background: In spite that chemoreception is important in sexual selection for many animals, such as reptiles, the mechanisms that confer reliability to chemical signals are relatively unknown. European green lizards (Lacerta viridis) have substantial amounts of a-tocopherol ( = vitamin E) in their femoral secretions. Because vitamin E is metabolically important and can only be attained from the diet, its secretion is assumed to be costly. However, its role in intraspecific communication is unknown.

Oecologia, 2008

) cost-benefit model of lizard thermoregulation predicts variation in thermoregulatory strategies... more ) cost-benefit model of lizard thermoregulation predicts variation in thermoregulatory strategies (from active thermoregulation to thermoconformity) with respect to the costs and benefits of the thermoregulatory behaviour and the thermal quality of the environment. Although this framework has been widely employed in correlative field studies, experimental tests aiming to evaluate the model are scarce. We conducted laboratory experiments to see whether the common lizard Zootoca vivipara, an active and effective thermoregulator in the field, can alter its thermoregulatory behaviour in response to differences in perceived predation risk and food supply in a constant thermal environment. Predation risk and food supply were represented by chemical cues of a sympatric snake predator and the lizards' food in the laboratory, respectively. We also compared males and postpartum females, which have different preferred or ''target'' body temperatures. Both sexes thermoregulated actively in all treatments. We detected sex-specific differences in the way lizards adjusted their accuracy of thermoregulation to the treatments: males were less accurate in the predation treatment, while no such effects were detected in females. Neither sex reacted to the food treatment. With regard to the two main types of thermoregulatory behaviour (activity and microhabitat selection), the treatments had no significant effects. However, postpartum females were more active than males in all treatments. Our results further stress that increasing physiological performance by active thermoregulation has high priority in lizard behaviour, but also shows that lizards can indeed shift their accuracy of thermoregulation in response to costs with possible immediate negative fitness effects (i.e. predation-caused mortality).

Naturwissenschaften, 2005

Interpopulation comparisons of variation in resource availability and in allocation patterns alon... more Interpopulation comparisons of variation in resource availability and in allocation patterns along altitudinal and latitudinal gradients allow insights into the mechanisms shaping the life history of animals. Patterns of between-population differences in female life history traits have been studied intensively across a wide range of taxa, but similar investigations in males have remained scarce. To study if testis weight-a measure of reproductive investment-varies on a geographical scale in anurans, we focussed on the variation in relative testis weight (RelTW) and asymmetry in 22 populations of the common frog Rana temporaria along a 1,600-km latitudinal transect across the Scandinavian peninsula. We found that RelTW decreased towards the north. Body mass and body length both had independent positive effects on testes mass. We found evidence for directional asymmetry (DA) in testis weight with the right testis being larger than the left. The level of DA in testis weight was not related to latitude, but both body mass and testes mass had independent positive effects on asymmetry. We discuss the northwards decrease in RelTW in terms of a decreased reproductive investment as a possi-A. Hettyey ( ) · G. Herczeg · T. Kovács ble consequence of harsher environmental conditions, and perhaps also, weaker sexual selection in the north than in the south.

Naturwissenschaften, 2004

Tail autotomy in lizards is an adaptive strategy that has evolved to reduce the risk of predation... more Tail autotomy in lizards is an adaptive strategy that has evolved to reduce the risk of predation. Since tail loss reduces body mass and moving ability-which in turn are expected to influence thermal balance-there is potential for a trade-off between tail autotomy and thermoregulation. To test this hypothesis, we studied a common lizard (Zootoca vivipara) population at high latitude, inhabiting a high-cost thermal environment. Z. vivipara is a small, non-territorial lizard known as a very accurate thermoregulator. We made two predictions: (1) the reduced body weight due to tail loss results in faster heating rate (a benefit), and (2) the reduction in locomotor ability after tail loss induces a shift to the use of thermally poorer microhabitats (a cost), thus decreasing the field body temperatures of active lizards. We did not find any effect of tail loss on heating rate in laboratory experiments conducted under different thermal conditions. Likewise, no significant relationship between tail condition and field body temperatures, or between tail condition and thermal microhabitat use, were detected. Thus, our results suggest that tail autotomy does not influ-ence the accuracy of thermoregulation in small-bodied lizards .

Molecular Ecology, 2010

The genetic structure of contemporary populations can be shaped by both their history and current... more The genetic structure of contemporary populations can be shaped by both their history and current ecological conditions. We assessed the relative importance of postglacial colonization history and habitat type in the patterns and degree of genetic diversity and differentiation in northern European nine-spined sticklebacks (Pungitius pungitius), using mitochondrial DNA (mtDNA) sequences and 12 nuclear microsatellite and insertion ⁄ deletion loci. The mtDNA analyses identified -and microsatellite analyses supported -the existence of two historically distinct lineages (eastern and western). The analyses of nuclear loci among 51 European sites revealed clear historically influenced and to minor degree habitat dependent, patterns of genetic diversity and differentiation. While the effect of habitat type on the levels of genetic variation (coastal > freshwater) and differentiation (freshwater > coastal) was clear, the levels of genetic variability and differentiation in the freshwater sites were independent of habitat type (viz. river, lake and pond). However, levels of genetic variability, together with estimates of historical effective population sizes, decreased dramatically and linearly with increasing latitude. These geographical patterns of genetic variability and differentiation suggest that the contemporary genetic structure of freshwater nine-spined sticklebacks has been strongly impacted by the founder events associated with postglacial colonization and less by current ecological conditions (cf. habitat type). In general, the results highlight the strong and persistent effects of postglacial colonization history on genetic structuring of northern European fauna and provide an unparalleled example of latitudinal trends in levels of genetic diversity.

Journal of Zoology, 2008

In vertebrates with genetic sex determination, large deviations from the 1:1 sex ratio at the pop... more In vertebrates with genetic sex determination, large deviations from the 1:1 sex ratio at the population level are rare and demand an explanation. We investigated adult sex-ratio variation of common frogs Rana temporaria in two subarctic breeding ponds over a 6-year (1999-2004) period using capture-mark-recapture (CMR) methods. Using the same data, we also tested for the occurrence of the biannual breeding cycle in female common frogs and sought evidence for population size decline. Sex ratios were highly female biased in both populations: on average, only about 30% of breeding individuals were males. CMR analyses further suggested that the female-biased sex ratio was not explainable by higher adult mortality among males as the survival probabilities over years were similar (c. 70%) for both sexes. Alternative explanations for these highly female-biased sex ratios include sex-specific mortality at earlier life stages and environmental influences on the sex determination system. While further studies are required to differentiate between the alternatives, the observed sex-ratio bias is among the strongest reported in any amphibian population so far, and also in the direction opposite to that usually observed (males4females). Our analyses found no support for the contention that female common frogs in northern populations may reproduce only in every second year. However, both study populations were declining during the study period.

Evolution, 2009

The relaxation of predation and interspecific competition are hypothesized to allow evolution tow... more The relaxation of predation and interspecific competition are hypothesized to allow evolution toward "optimal" body size in island environments, resulting in the gigantism of small organisms. We tested this hypothesis by studying a small teleost (ninespined stickleback, Pungitius pungitius) from four marine and five lake (diverse fish community) and nine pond (impoverished fish community) populations. In line with theory, pond fish tended to be larger than their marine or lake conspecifics, sometimes reaching giant sizes. In two geographically independent cases when predatory fish had been introduced into ponds, fish were smaller than those in nearby ponds lacking predators. Pond fish were also smaller when found in sympatry with three-spined stickleback (Gasterosteus aculeatus) than those in ponds lacking competitors. Size-at-age analyses demonstrated that larger size in ponds was achieved by both increased growth rates and extended longevity of pond fish. Results from a common garden experiment indicate that the growth differences had a genetic basis: pond fish developed two to three times higher body mass than marine fish during 36 weeks of growth under similar conditions. Hence, reduced risk of predation and interspecific competition appear to be chief forces driving insular body size evolution toward gigantism.

BMC Evolutionary Biology, 2010

The thermal benefits of melanism in ectothermic animals are widely recognized, but relatively lit... more The thermal benefits of melanism in ectothermic animals are widely recognized, but relatively little is known about population differentiation in the degree of melanism along thermal gradients, and the relative contributions of genetic vs. environmental components into the level of melanism expressed. We investigated variation in the degree of melanism in the common frog (Rana temporaria; an active heliotherm thermoregulator) by comparing the degree of melanism (i) among twelve populations spanning over 1500 km long latitudinal gradient across the Scandinavian Peninsula and (ii) between two populations from latitudinal extremes subjected to larval temperature treatments in a common garden experiment.

Biological Journal of the Linnean Society, 2010

Parallel evolution is characterised by repeated, independent occurrences of similar phenotypes in... more Parallel evolution is characterised by repeated, independent occurrences of similar phenotypes in a given habitat type, in different parts of the species distribution area. We studied body shape and body armour divergence between five marine, four lake, and ten pond populations of nine-spined sticklebacks [Pungitius pungitius (Linnaeus, 1758)] in Fennoscandia. We hypothesized that marine and lake populations (large water bodies, diverse fish fauna) would be similar, whereas sticklebacks in isolated ponds (small water bodies, simple fish fauna) would be divergent. We found that pond fish had deeper bodies, shorter caudal peduncles, and less body armour (viz. shorter/absent pelvic spines, reduced/absent pelvic girdle, and reduced number of lateral plates) than marine fish. Lake fish were intermediate, but more similar to marine than to pond fish. Results of our common garden experiment concurred with these patterns, suggesting a genetic basis for the observed divergence. We also found large variation among populations within habitat types, indicating that environmental variables other than those related to gross habitat characteristics might also influence nine-spined stickleback morphology. Apart from suggesting parallel evolution of morphological characteristics of nine-spined sticklebacks in different habitats, the results also show a number of similarities to the evolution of three-spined stickleback (Gasterosteus aculeatus Linnaeus, 1758) morphology.

Biologia, 2007

Microhabitat selection and seasonal activity of the snake-eyed skink, Ablephaus kitaibelii fitzin... more Microhabitat selection and seasonal activity of the snake-eyed skink, Ablephaus kitaibelii fitzingeri, are compared to the two lacertid lizards (Lacerta viridis and Podarcis muralis) that co-occur in many of its habitats. The food composition of A. k. fitzingeri is also described. Significant differences in microhabitat selection and seasonal activity among the three species were found. The snake-eyed skink was associated with open grasslands, and with a low level of scrub, bare soil and rock cover. The microhabitat preference of L. viridis was quite similar to that of the skink, but with a higher preference for scrub. P. muralis occurred in places with greater rock and bare soil cover, and more scrub than A. k. fitzingeri. Activity of the snake-eyed skink decreased dramatically in summer, probably because of the reduced thermal inertia originating from the extremely small size of this species, but its seasonal activity overlapped with those of the lacertids. Stomach content analysis of the snake-eyed skink suggests that it is a generalist predator of small, mainly flightless arthropod prey. Competition with juvenile lacertids and predation by adult L. viridis are conceivable for the snake-eyed skink.