In search of a general theory of species’ range evolution

Authors: Tim Connallon and Carla M Sgrò

Published in: PLoS Biology


Despite the pervasiveness of the world’s biodiversity, no single species has a truly global distribution. In fact, most species have very restricted distributions. What limits species from expanding beyond their current geographic ranges?

This has been classically treated by ecologists as an ecological problem and by evolutionary biologists as an evolutionary problem. Such a dichotomy is false — the problem of species’ ranges sits firmly within the realm of evolutionary ecology.

In support of this view, Polechová presents new theory that explains species’ range limits with reference to two key factors central to both ecological and evolutionary theory—migration and population size.

This new model sets the scene for empirical tests of range limit theory and builds the case for assisted gene flow as a key management tool for threatened species.


Connallon T, Sgrò CM (2018) In search of a general theory of species’ range evolution, PLoS Biology. PDF DOI

Evidence for lower plasticity in CT-MAX at warmer developmental temperatures

Authors: Vanessa Kellermann and Carla M. Sgrò

Published in: Journal of Evolutionary Biology


Understanding the capacity for different species to reduce their susceptibility to climate change via phenotypic plasticity is essential for accurately predicting species extinction risk.

The climatic variability hypothesis suggests that spatial and temporal variation in climatic variables should select for more plastic phenotypes. However, empirical support for this hypothesis is limited.

Here, we examine the capacity for ten Drosophila species to increase their critical thermal maxima (CTMAX) through developmental acclimation and/or adult heat hardening.

Using four fluctuating developmental temperature regimes, ranging from 13 to 33  °C, we find that most species can increase their CTMAX via developmental acclimation and adult hardening, but found no relationship between climatic variables and absolute measures of plasticity. However, when plasticity was dissected across developmental temperatures, a positive association between plasticity and one measure of climatic variability (temperature seasonality) was found when development took place between 26 and 28 °C, whereas a negative relationship was found when development took place between 20 and 23  °C.

In addition, a decline in CTMAX and egg‐to‐adult viability, a proxy for fitness, was observed in tropical species at the warmer developmental temperatures (26–28 °C); this suggests that tropical species may be at even greater risk from climate change than currently predicted. The combined effects of developmental acclimation and adult hardening on CTMAX were small, contributing to a <0.60 °C shift in CTMAX.

Although small shifts in CTMAX may increase population persistence in the shorter term, the degree to which they can contribute to meaningful responses in the long term is unclear.


Kellermann V, Sgrò CM (2018) Evidence for lower plasticity in CTMAX at warmer developmental temperatures. Journal of Evolutionary BiologyPDF DOI

Cross‐sex genetic correlations and the evolution of sex‐specific local adaptation: Insights from classical trait clines in Drosophila melanogaster

Authors: Clémentine Lasne, Sandra B Hangartner, Tim Connallon, and Carla M. Sgrò

Published in: Evolution


Natural selection varies widely among locations of a species’ range, favoring population divergence and adaptation to local environmental conditions. Selection also differs between females and males, favoring the evolution of sexual dimorphism. Both forms of within‐species evolutionary diversification are widely studied, though largely in isolation, and it remains unclear whether environmental variability typically generates similar or distinct patterns of selection on each sex.

Studies of sex‐specific local adaptation are also challenging because they must account for genetic correlations between female and male traits, which may lead to correlated patterns of trait divergence between sexes, whether or not local selection patterns are aligned or differ between the sexes.

We quantified sex‐specific divergence in five clinally variable traits in Drosophila melanogasterthat individually vary in their magnitude of cross‐sex genetic correlation (i.e., from moderate to strongly positive).

In all five traits, we observed parallel male and female clines, regardless of the magnitude of their genetic correlation. These patterns imply that parallel spatial divergence of female and male traits is a reflection of sexually concordant directional selection imposed by local environmental conditions. In such contexts, genetic correlations between the sexes promote, rather than constrain, local adaptation to a spatially variable environment.


Lasne C, Hangartner SB, Connallon T, Sgrò CM (2018) Cross-sex genetic correlations and the evolution of sex-specific local adaptation: Insights from classical trait clines in Drosophila melanogaster, Evolution PDF DOI

Understanding managers’ and scientists’ perspectives on opportunities to achieve more evolutionarily enlightened management in conservation

Authors: Carly N Cook and Carla M Sgrò

Published in: Evolutionary Applications


Despite wide acceptance that conservation could benefit from greater attention to principles and processes from evolutionary biology, little attention has been given to quantifying the degree to which relevant evolutionary concepts are being integrated into management practices. There has also been increasing discussion of the potential reasons for a lack of evolutionarily enlightened management, but no attempts to understand the challenges from the perspective of those making management decisions.

In this study, we asked conservation managers and scientists for their views on the importance of a range of key evolutionary concepts, the degree to which these concepts are being integrated into management, and what would need to change to support better integration into management practices.

We found that while managers recognize the importance of a wide range of evolutionary concepts for conservation outcomes, they acknowledge these concepts are rarely incorporated into management. Managers and scientists were in strong agreement about the range of barriers that need to be overcome, with a lack of knowledge reported as the most important barrier to better integration of evolutionary biology into conservation decision‐making.

Although managers tended to be more focused on the need for more training in evolutionary biology, scientists reported greater engagement between managers and evolutionary biologists as most important to achieve the necessary change. Nevertheless, the challenges appear to be multifaceted, and several are outside the control of managers, suggesting solutions will need to be multidimensional.


Cook CN, Sgrò CM (2018) Understanding managers’ and scientists’ perspectives on opportunities to achieve more evolutionarily enlightened management in conservation, Evolutionary Applications. PDF DOI

Plasticity for desiccation tolerance across Drosophila species is affected by phylogeny and climate in complex ways

Authors: Vanessa Kellermann, Ary A Hoffmann, Johannes Overgaard, Volker Loeschcke, and Carla M Sgrò

Published in: Proceedings of the Royal Society B: Biological Sciences


Comparative analyses of ectotherm susceptibility to climate change often focus on thermal extremes, yet responses to aridity may be equally important.

Here we focus on plasticity in desiccation resistance, a key trait shaping distributions of Drosophila species and other small ectotherms.

We examined the extent to which 32 Drosophila species, varying in their distribution, could increase their desiccation resistance via phenotypic plasticity involving hardening, linking these responses to environment, phylogeny and basal resistance.

We found no evidence to support the seasonality hypothesis; species with higher hardening plasticity did not occupy environments with higher and more seasonal precipitation. As basal resistance increased, the capacity of species to respond via phenotypic plasticity decreased, suggesting plastic responses involving hardening may be constrained by basal resistance. Trade-offs between basal desiccation resistance and plasticity were not universal across the phylogeny and tended to occur within specific clades. Phylogeny, environment and trade-offs all helped to explain variation in plasticity for desiccation resistance but in complex ways.

These findings suggest some species have the ability to counter dry periods through plastic responses, whereas others do not; and this ability will depend to some extent on a species’ placement within a phylogeny, along with its basal level of resistance.


Kellermann V, Hoffmann AA, Overgaard J, Loeschcke V, Sgrò CM (2018) Plasticity for desiccation tolerance across Drosophila species is affected by phylogeny and climate in complex ways. Proceedings of the Royal Society B: Biological Sciences. PDF DOI

Artificial barriers prevent genetic recovery of small isolated populations of a low-mobility freshwater fish

Authors: Rhys A Coleman, Bertrand Gauffre, Anna Pavlova, Luciano  B Beheregaray, Joanne Kearns, Jarod Lyon, Minami Sasaki, Raphael Leblois, Carla M Sgrò, and Paul Sunnucks

Published in: Heredity


Habitat loss and fragmentation often result in small, isolated populations vulnerable to environmental disturbance and loss of genetic diversity. Low genetic diversity can increase extinction risk of small populations by elevating inbreeding and inbreeding depression, and reducing adaptive potential. Due to their linear nature and extensive use by humans, freshwater ecosystems are especially vulnerable to habitat loss and fragmentation.

Although the effects of fragmentation on genetic structure have been extensively studied in migratory fishes, they are less understood in low-mobility species.

We estimated impacts of instream barriers on genetic structure and diversity of the low-mobility river blackfish (Gadopsis marmoratus) within five streams separated by weirs or dams constructed 45–120 years ago.

We found evidence of small-scale (<13 km) genetic structure within reaches unimpeded by barriers, as expected for a fish with low mobility. Genetic diversity was lower above barriers in small streams only, regardless of barrier age. In particular, one isolated population showed evidence of a recent bottleneck and inbreeding. Differentiation above and below the barrier (FST = 0.13) was greatest in this stream, but in other streams did not differ from background levels.

Spatially explicit simulations suggest that short-term barrier effects would not be detected with our data set unless effective population sizes were very small (<100).

Our study highlights that, in structured populations, the ability to detect short-term genetic effects from barriers is reduced and requires more genetic markers compared to panmictic populations. We also demonstrate the importance of accounting for natural population genetic structure in fragmentation studies.


Coleman RA, Gauffre B, Pavlova A, Beheregaray LB, Kearns J, Lyon J, Sasaki M, Leblois R, Sgro C, Sunnucks P (2018) Artificial barriers prevent genetic recovery of small isolated populations of a low-mobility freshwater fish. Heredity PDF DOI

Basal resistance enhances warming tolerance of alien over indigenous species across latitude

Authors: Charlene Janion-Scheepers, Laura Phillips, Carla M Sgrò, Grant A Duffy, Rebecca Hallas, and Steven L Chown

Published in: Proceedings of the National Academy of Sciences of the United States of America, volume 115, issue 1


Soil systems are being increasingly exposed to the interactive effects of biological invasions and climate change, with rising temperatures expected to benefit alien over indigenous species.

We assessed this expectation for an important soil-dwelling group, the springtails, by determining whether alien species show broader thermal tolerance limits and greater tolerance to climate warming than their indigenous counterparts.

We found that, from the tropics to the sub-Antarctic, alien species have the broadest thermal tolerances and greatest tolerance to environmental warming. Both groups of species show little phenotypic plasticity or potential for evolutionary change in tolerance to high temperature.

These trait differences between alien and indigenous species suggest that biological invasions will exacerbate the impacts of climate change on soil systems, with profound implications for terrestrial ecosystem functioning.


Janion-Scheepers C, Phillips L, Sgrò CM, Duffy GA, Hallas R, Chown SL (2018) Basal resistance enhances warming tolerance of alien over indigenous species across latitude. Proceedings of the National Academy of Sciences of the United States of America PDF DOI

Comparative studies of critical physiological limits and vulnerability to environmental extremes in small ectotherms: How much environmental control is needed?

Authors: Ary A Hoffmann and Carla M Sgrò

Published in: Integrative Zoology, volume 13, issue 4 (July 2018)


Researchers and practitioners are increasingly using comparative assessments of critical thermal and physiological limits to assess the relative vulnerability of ectothermic species to extreme thermal and aridity conditions occurring under climate change.

In most assessments of vulnerability, critical limits are compared across taxa exposed to different environmental and developmental conditions. However, many aspects of vulnerability should ideally be compared when species are exposed to the same environmental conditions, allowing a partitioning of sources of variation such as used in quantitative genetics.

This is particularly important when assessing the importance of different types of plasticity to critical limits, using phylogenetic analyses to test for evolutionary constraints, isolating genetic variants that contribute to limits, characterizing evolutionary interactions among traits limiting adaptive responses, and when assessing the role of cross generation effects. However, vulnerability assessments based on critical thermal/physiological limits also need to take place within a context that is relevant to field conditions, which is not easily provided under controlled environmental conditions where behavior, microhabitat, stress exposure rates and other factors will differ from field conditions.

There are ways of reconciling these requirements, such as by taking organisms from controlled environments and then testing their performance under field conditions (or vice versa).

While comparisons under controlled environments are challenging for many taxa, assessments of critical thermal limits and vulnerability will always be incomplete unless environmental effects within and across generations are considered, and where the ecological relevance of assays measuring critical limits can be established.


Hoffmann AA, Sgrò CM (2018) Comparative studies of critical physiological limits and vulnerability to environmental extremes in small ectotherms: How much environmental control is needed? Integrative Zoology PDF DOI

Transcriptional profiles of plasticity for desiccation stress in Drosophila

Authors: Allannah S Clemson, Carla M Sgrò, and Marina Telonis-Scott

Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology


We examined the transcriptional responses of desiccation resistance candidate genes in populations of Drosophila melanogaster divergent for desiccation resistance and in capacity to improve resistance via phenotypic plasticity.

Adult females from temperate and tropical eastern Australian populations were exposed to a rapid desiccation hardening (RDH) treatment, and groups without RDH to acute desiccation stress, and the transcript expression of 12 candidate desiccation genes were temporally profiled during, and in recovery from stress.

We found that desiccation exposure resulted in largely transitory, stress-specific transcriptional changes in all but one gene. However linking the expression profiles to the population-level phenotypic divergence was difficult given subtle, and time-point specific population expression variation. Nonetheless, rapid desiccation hardening had the largest effect on gene expression, resulting in distinct molecular profiles.

We report a hitherto uncharacterised desiccation molecular hardening response where prior exposure essentially ‘primes’ genes to respond to subsequent stress without discernible transcript changes prior to stress. This, taken together with some population gene expression variation of several bona fide desiccation candidates associated with different water balance strategies speaks of the complexity of natural desiccation resistance and plasticity and provides new avenues for understanding the molecular basis of a trait of ecological significance.


Clemson AS, Sgrò CM, Telonis-Scott M (2018) Transcriptional profiles of plasticity for desiccation stress in Drosophila, Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology PDF DOI

The quantitative genetic basis of clinal divergence in phenotypic plasticity

Authors: Belinda van Heerwaarden and Carla M Sgrò

Published in: Evolution


Phenotypic plasticity is thought to be an important mechanism for adapting to environmental heterogeneity. Nonetheless, the genetic basis of plasticity is still not well understood.

In Drosophila melanogaster and D. simulans, body size and thermal stress resistance show clinal patterns along the east coast of Australia, and exhibit plastic responses to different developmental temperatures. The genetic basis of thermal plasticity, and whether the genetic effects underlying clinal variation in traits and their plasticity are similar, remains unknown.

Here, we use line‐cross analyses between a tropical and temperate population of Drosophila melanogaster and D. simulans developed at three constant temperatures (18°C, 25°C, and 29°C) to investigate the quantitative genetic basis of clinal divergence in mean thermal response (elevation) and plasticity (slope and curvature) for thermal stress and body size traits.

Generally, the genetic effects underlying divergence in mean response and plasticity differed, suggesting that different genetic models may be required to understand the evolution of trait means and plasticity.

Furthermore, our results suggest that nonadditive genetic effects, in particular epistasis, may commonly underlie plastic responses, indicating that current models that ignore epistasis may be insufficient to understand and predict evolutionary responses to environmental change.


van Heerwaarden B, Sgrò CM (2017) The quantitative genetic basis of clinal divergence in phenotypic plasticity, Evolution PDF DOI