Grazer commensalism varies across the species range edge: host size influences epibiont incidence and spatial segregation

Species’ geographic ranges and climatic niches are likely to be increasingly mismatched due to rapid climate change. If a species’ range and niche are out of equilibrium, then population performance should decrease from high-latitude “leading” range edges, where populations are expanding into recently ameliorated habitats, to low-latitude “trailing” range edges, where populations are contracting from newly unsuitable areas. Demographic compensation is a phenomenon whereby declines in some vital rates are offset by increases in others across time or space. In theory, demographic compensation could increase the range of environments over which populations can succeed and forestall range contraction at trailing edges. An outstanding question is whether range limits and range contractions reflect inadequate demographic compensation across environmental gradients, causing population declines at range edges. We collected demographic data from 32 populations of the scarlet monkeyflower (Erythranthe cardinalis) spanning 11° of latitude in western North America and used integral projection models to evaluate population dynamics and assess demographic compensation across the species’ range. During the 5-y study period, which included multiple years of severe drought and warming, population growth rates decreased from north to south, consistent with leading-trailing dynamics. Southern populations at the trailing range edge declined due to reduced survival, growth, and recruitment, despite compensatory increases in reproduction and faster life-history characteristics. These results suggest that demographic compensation may only delay population collapse without the return of more favorable conditions or the contribution of other buffering mechanisms such as evolutionary rescue.

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Evolutionary ecology at the extremes of species’ ranges

Environmental Reviews ◽

10.1139/a09-014 ◽

2010 ◽

Vol 18 (NA) ◽

pp. 1-20 ◽

Cited By ~ 112

Author(s):

David C. Hardie ◽

Jeffrey A. Hutchings

Keyword(s):

Evolutionary Ecology ◽

Extinction Risk ◽

Species Range ◽

Local Extinction ◽

Peripheral Populations ◽

Species Ranges ◽

Evolutionary Forces ◽

Range Edge ◽

Evolutionary Innovation ◽

Abiotic Stressors

The nature of species at the extremes of their ranges impinges fundamentally on diverse biological issues, including species’ range dynamics, population variability, speciation and conservation biology. We review the literature concerning genetic and ecological variation at species’ range edges, and discuss historical and contemporary forces that may generate observed trends, as well as their current and future implications. We discuss literature which shows how environmental, ecological and evolutionary factors act to limit species’ ranges, and how these factors impose selection for adaptation or dispersal in peripheral populations exposed to extreme and stochastic biotic and abiotic stressors. When conditions are sufficiently harsh such that local extinction is certain, peripheral populations may represent temporary offshoots from stable core populations. However, in cases where peripheral populations persist at the range edge under divergent or extreme conditions, biologically significant differences can arise from historical and contemporary ecological and evolutionary forces. In many such cases reviewed herein, peripheral populations tended to diverge from the species’ core, and to display lower genetic diversity or greater stress-adaptation. We conclude that while such populations may be of particular conservation value as significant components of intraspecific biodiversity or sources of evolutionary innovation and persistence during environmental change, small and greatly variable population size, especially combined with low genetic variability, can result in elevated extinction risk in harsh and stochastic peripheral environments. As a result, while peripheral populations should not be dismissed as evolutionary dead-ends destined for local extinction, neither should they be uncritically granted inherently superior significance based only on their peripheral position alone.

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Gene swamping alters evolution during range expansions in the protist Tetrahymena thermophila

Biology Letters ◽

10.1098/rsbl.2020.0244 ◽

2020 ◽

Vol 16 (6) ◽

pp. 20200244

Author(s):

Felix Moerman ◽

Emanuel A. Fronhofer ◽

Andreas Wagner ◽

Florian Altermatt

Keyword(s):

Genetic Variation ◽

Gene Flow ◽

Tetrahymena Thermophila ◽

Species Range ◽

Ph Gradient ◽

Life History Strategies ◽

Range Edge ◽

Asymmetric Dispersal ◽

Accelerated Evolution ◽

Range Core

At species’ range edges, individuals often face novel environmental conditions that may limit range expansion until populations adapt. The potential to adapt depends on genetic variation upon which selection can act. However, populations at species’ range edges are often genetically depauperate. One mechanism increasing genetic variation is reshuffling existing variation through sex. Sex, however, can potentially limit adaptation by breaking up existing beneficial allele combinations (recombination load). The gene swamping hypothesis predicts this is specifically the case when populations expand along an abiotic gradient and asymmetric dispersal leads to numerous maladapted dispersers from the range core swamping the range edge. We used the ciliate Tetrahymena thermophila as a model for testing the gene swamping hypothesis. We performed replicated range expansions in landscapes with or without a pH-gradient, while simultaneously manipulating the occurrence of gene flow and sexual versus asexual reproduction. We show that sex accelerated evolution of local adaptation in the absence of gene flow, but hindered it in the presence of gene flow. However, sex affected adaptation independently of the pH-gradient, indicating that both abiotic gradients and the biotic gradient in population density lead to gene swamping. Overall, our results show that gene swamping alters adaptation in life-history strategies.

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Ectomycorrhizal fungal richness declines towards the host species’ range edge

Molecular Ecology ◽

10.1111/mec.13628 ◽

2016 ◽

Vol 25 (13) ◽

pp. 3224-3241 ◽

Cited By ~ 17

Author(s):

Richard A. Lankau ◽

Daniel P. Keymer

Keyword(s):

Host Species ◽

Species Range ◽

Range Edge

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Genomic signatures of spatially divergent selection at clownfish range margins

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2021.0407 ◽

2021 ◽

Vol 288 (1952) ◽

pp. 20210407

Author(s):

René D. Clark ◽

Matthew L. Aardema ◽

Peter Andolfatto ◽

Paul H. Barber ◽

Akihisa Hattori ◽

...

Keyword(s):

Gene Flow ◽

Candidate Genes ◽

Local Adaptation ◽

Genetic Drift ◽

Divergent Selection ◽

Species Range ◽

Evolutionary Forces ◽

The Core ◽

Range Edge ◽

Genomic Signatures

Understanding how evolutionary forces interact to drive patterns of selection and distribute genetic variation across a species' range is of great interest in ecology and evolution, especially in an era of global change. While theory predicts how and when populations at range margins are likely to undergo local adaptation, empirical evidence testing these models remains sparse. Here, we address this knowledge gap by investigating the relationship between selection, gene flow and genetic drift in the yellowtail clownfish, Amphiprion clarkii, from the core to the northern periphery of the species range. Analyses reveal low genetic diversity at the range edge, gene flow from the core to the edge and genomic signatures of local adaptation at 56 single nucleotide polymorphisms in 25 candidate genes, most of which are significantly correlated with minimum annual sea surface temperature. Several of these candidate genes play a role in functions that are upregulated during cold stress, including protein turnover, metabolism and translation. Our results illustrate how spatially divergent selection spanning the range core to the periphery can occur despite the potential for strong genetic drift at the range edge and moderate gene flow from the core populations.

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Steppe rodents at the edge of their range: A case study of Spalax microphthalmus in the north of Ukraine

Biosystems Diversity ◽

10.15421/011829 ◽

2018 ◽

Vol 26 (3) ◽

pp. 188-200 ◽

Cited By ~ 3

Author(s):

I. Zagorodniuk ◽

M. Korobchenko ◽

V. Parkhomenko ◽

Z. Barkaszi

Keyword(s):

Field Research ◽

Common Species ◽

Species Range ◽

Forest Steppe ◽

Natural Habitats ◽

The West ◽

Range Edge ◽

Mole Rat ◽

Central Russian Upland ◽

Arable Farming

Based on results obtained during 2000–2018 by field research, polls of colleagues, and OSINT analysis, features of distribution of the greater mole rat Spalax microphthalmus in the eastern forest steppe of Ukraine were considered. The studied part of the species’ range is unique and represents the northern range edge of the entire Spalacidae family and of European steppe faunal assemblages in general. In total, data on 146 record localities were amassed, including 13 localities in the fragmented and 133 in the continuous part of the range. The offshoots of the Central Russian Upland in the valley of the Psel river (east of Sumy Oblast) are the sites with the highest density of settlements, while the species’ type biotopes are steppe balka slopes. The abundance of the greater mole rat decreased from the east to the west, and its colonies are the most fragmented along the Dnipro River. The species occurs in steppe and meadow habitats of an area of at least 20–50 ha. Analysis of the current and former distribution of the greater mole rat revealed that the species range contracts from the west; earlier it was a common species in different regions of the Middle Dnipro Area (including Kyiv city), but the current range edge runs along the line connecting Buryn – Nedryhailiv – Lokhvytsia – Myrhorod – Hadiach – Zinkiv – Zaliznychne. Isolated settlements exist in adjacent territories, particularly in Ichnia Raion of Chernihiv Oblast, and Lubny, Khorol, and Kobeliaky Raions of Poltava Oblast. The study showed that the species’ range contracted by two times to 35,000 km2 for the last 100 years, which includes only 430,000 ha of suitable habitats (15% of the range), allowing the existence here of 86,000–215,000 individuals. In fact, the species remained only in habitats that have been minimally affected by arable farming and other forms of active agricultural use. Besides, the species shows a clear confinement to habitats located near human settlements such as untilled lands, pastures with moderate grazing, waste and neglected lands, which constitute a separate group of transformed and semi-natural habitats. Formally, this allows the greater mole rat to be considered as a synanthropic species, because its inhabited biotopes, beside the zone of offshoots of the Central Russian Upland, have remained only near villages and along roads. The species also has an important biocoenotic role due to its burrowing activity and as prey of predatory birds (e.g., of the long-legged buzzard and Eurasian eagle owl) and mammals. The feeding period of the offspring of these predators generally coincides with the aboveground activity of mole rats, which lasts during May–July with a peak in June. Aboveground activity is mainly related to the resettlement of mole rats to new sites and dispersal of the young, due to which they became victims of predators.

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Gene swamping alters evolution during range expansions in the protist Tetrahymena thermophila

10.1101/863340 ◽

2019 ◽

Author(s):

Felix Moerman ◽

Emanuel A. Fronhofer ◽

Andreas Wagner ◽

Florian Altermatt

Keyword(s):

Genetic Variation ◽

Gene Flow ◽

Tetrahymena Thermophila ◽

Species Range ◽

Ph Gradient ◽

Life History Strategies ◽

Range Edge ◽

Asymmetric Dispersal ◽

Accelerated Evolution ◽

Range Core

AbstractAt species’ range edges, individuals often face novel environmental conditions that may limit range expansion until populations adapt. The potential to adapt depends on genetic variation upon which selection can act. However, populations at species’ range edges are often genetically depauperated. One mechanism to increase genetic variation is to reshuffle existing variation through sex. During range expansions, sex can, however, act as a double-edged sword. The gene swamping hypothesis predicts that for populations expanding along an abiotic gradient, sex can hinder adaptation if asymmetric dispersal leads to numerous maladapted dispersers from the range core swamping the range edge. In this study, we experimentally tested the gene swamping hypothesis by performing replicated range expansions in landscapes with or without an abiotic pH-gradient, using the ciliate Tetrahymena thermophila, while simultaneously manipulating the occurrence of gene flow and sex. We show that sex accelerated evolution of local adaptation in the absence of gene flow, but hindered it in the presence of gene flow. The effect of sex, however, was independent of the pH-gradient, indicating that not only abiotic gradients but also the biotic gradient in population density leads to gene swamping. Overall, our results show that gene swamping can affect adaptation in life-history strategies.

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