Biology subjects

Unmack, P.

Publications and source records attributed to Unmack, P..

6 recordsLinked to original sources

bioRxiv2026

From tropical rainforests to scorching deserts: biogeography shapes climate-change plasticity in Australian rainbowfishes

Thermal tolerance and the plasticity of regulatory mechanisms are likely to influence biodiversity persistence under global warming. Continental-scale assessments of physiological resilience and gene expression plasticity within a closely related clade are rare, yet they could reveal how bioregional climatic history shapes vulnerability to climate warming. We used a comparative approach across five climatic ecotypes of Australian rainbowfishes (tropical rainforest, tropical savannah, subtropical, desert, and temperate) to investigate variation in thermal tolerance and gene expression plasticity in response to warming. We reconstructed phylogenetic relationships among these ecotypes, estimated their ecological niches and environmental warming tolerance, and experimentally measured CTMAX and global gene expression responses to a projected summer heat event. Closely related ecotypes showed divergent bioclimatic niches, contrasting sensitivities to warming, and extensive but idiosyncratic expression responses to heat stress. Plastic responses to warming, including in key heat stress genes, were positively associated with thermal tolerance across ecotypes. The tropical savannah and subtropical ecotypes, both from environmentally variable bioregions, showed extensive transcriptional responses to warming and high thermal tolerance. The desert ecotype was intermediate for both traits, whereas the temperate ecotype showed the most limited transcriptional response and lowest thermal tolerance. In contrast, the tropical rainforest ecotype showed limited plasticity, potentially reflecting local adaptation to milder, more stable conditions and more specialised thermal responses. Our findings support the hypothesis that bioregional climatic history shapes broad patterns of climate resilience, including thermal tolerance and transcriptional plasticity, and may influence which combinations of traits are favoured under future climates.

ecology↗

bioRxiv2026

Tropical rainforest versus savannah: Biome-specific landscape structure mediates adaptive strategies and resilience to environmental change

As ecosystems face rapid environmental change, understanding the interplay between landscape structure, genetic diversity, and adaptive potential is critical for predicting resilience. We investigated how biome-specific connectivity and environmental heterogeneity mediate adaptive strategies and resilience in the tropical rainbowfish (Melanotaenia splendida splendida) across contrasting rainforest and savannah ecosystems in tropical Australia. Using an integrative framework combining genomic, morphological, and environmental analyses, we inferred that hydroclimatic variation has been a key driver of genetic and phenotypic divergence. Rainforest populations exhibited strong local adaptation to fragmented, stable environments, while savannah populations showed less genomic differentiation and morphological divergence, patterns consistent with weaker local adaptation. We hypothesise that greater reliance on phenotypic plasticity may facilitate adaptive responses in savannah populations, reflecting their exposure to more connected and variable environments. Variance partitioning highlighted the contrasting roles of neutral and adaptive processes across biomes, with implications for managing resilience in freshwater systems under climate change. Our findings underscore the trade-offs between connectivity, local adaptation, and plasticity, providing a model for understanding adaptation and resilience across diverse ecosystems.

ecology↗

bioRxiv2022

Natural hybridisation reduces vulnerability to climate change

Understanding how species can respond to climate change is a major global challenge. Species unable to track their niche via range shifts are largely reliant on genetic variation to adapt and persist. Genomic vulnerability predictions are used to identify populations that lack the necessary variation, particularly at climate relevant genes. However, hybridization as a source of novel adaptive variation is typically ignored in genomic vulnerability studies. We estimated environmental niche models and genomic vulnerability for closely related species of rainbowfish (Melanotaenia spp.) across an elevational gradient in the Australian wet tropics. Hybrid populations between a widespread generalist and narrow range endemics exhibited reduced vulnerability to projected climates compared to pure narrow endemics. Overlaps between introgressed and adaptive genomic regions were consistent with a signal of adaptive introgression. Our findings highlight the often-underappreciated conservation value of hybrid populations and indicate that adaptive introgression may contribute to evolutionary rescue of species with narrow environmental ranges.

evolutionary biology↗

bioRxiv2022

Environmental selection, rather than neutral processes, best explain patterns of diversity in a tropical rainforest fish

To conserve the high functional and genetic variation in hotspots such as tropical rainforests, it is essential to understand the forces driving and maintaining biodiversity. We asked to what extent environmental gradients and terrain structure affect morphological and genomic variation across the wet tropical distribution of an Australian rainbowfish, Melanotaenia splendida splendida. We used an integrative riverscape genomics and morphometrics framework to assess the influence of these factors on both putative adaptive and non-adaptive spatial divergence. We found that neutral genetic population structure was largely explainable by restricted gene flow among drainages. However, environmental associations revealed that ecological variables had a similar power to explain overall genetic variation, and greater power to explain body shape variation, than the included neutral covariables. Hydrological and thermal variables were the best environmental predictors and were correlated with traits previously linked to heritable habitat-associated dimorphism in rainbowfishes. Additionally, climate-associated genetic variation was significantly associated with morphology, supporting heritability of shape variation. These results support the inference of evolved functional differences among localities, and the importance of hydroclimate in early stages of diversification. We expect that substantial evolutionary responses will be required in tropical rainforest endemics to mitigate local fitness losses due to changing climates.

evolutionary biology↗

bioRxiv2021

Variation in intraspecific demography drives localised concordance but species-wide discordance in responses to Plio-Pleistocene climatic change

Understanding how species biology may facilitate resilience to climate change remains a critical factor in detecting and protecting species at risk of extinction. Many studies have focused on the role of particular ecological traits in driving species responses, but less so on demographic history and levels of standing genetic variation. We used environmental and genomic datasets to reconstruct the phylogeographic histories of two ecologically similar and largely co-distributed freshwater fishes to assess the degree of concordance in their responses to Plio-Pleistocene climatic changes. Although several co-occurring populations demonstrated concordant demographic histories, idiosyncratic population size changes were found at the range edges of the more spatially restricted species. Discordant responses between species were associated with low standing genetic variation in peripheral populations. This might have hindered adaptive potential, as documented in recent population declines and extinctions of the two species. Our results highlight both the role of spatial scale in the degree of concordance in species responses to climate change, and the importance of standing genetic variation in facilitating range shifts. Even when ecological traits are similar between species, long-term genetic diversity and historical population demography may lead to discordant responses to ongoing and future climate change.

evolutionary biology↗

bioRxiv2020

The roles of aridification and sea level changes in the diversification and persistence of freshwater fish lineages

While the influence of Pleistocene climatic changes on divergence and speciation has been well-documented across the globe, complex spatial interactions between hydrology and eustatics over longer timeframes may also determine species evolutionary trajectories. Within the Australian continent, glacial cycles were not associated with changes in ice cover and instead largely resulted in fluctuations from moist to arid conditions across the landscape. Here, we investigate the role of hydrological and coastal topographic changes brought about by Plio-Pleistocene climatic changes on the biogeographic history of a small Australian freshwater fish, the southern pygmy perch Nannoperca australis. Using 7,958 ddRAD-seq (double digest restriction-site associated DNA) loci and 45,104 filtered SNPs, we combined phylogenetic, coalescent and species distribution analyses to investigate the relative roles of aridification, sea level and tectonics and their associated biogeographic changes across southeast Australia. Sea-level changes since the Pliocene and reduction or disappearance of large waterbodies throughout the Pleistocene were determining factors in strong divergence across the clade, including the initial formation and maintenance of a cryptic species, N. flindersi. Isolated climatic refugia and fragmentation due to lack of connected waterways maintained the identity and divergence of inter- and intraspecific lineages. Our historical findings suggest that predicted increases in aridification and sea level due to anthropogenic climate change might result in markedly different demographic impacts, both spatially and across different landscape types.

evolutionary biology↗