Biology subjects

Bradford, T.

Publications and source records attributed to Bradford, T..

4 recordsLinked to original sources

bioRxiv2025

Nesting behaviour drives the evolution of heat tolerance and climate vulnerability in bees

Species vulnerability to climate change depends in part on their capacity to evolve in response to increasing heat1. Within terrestrial ectotherms, heat tolerance generally corresponds weakly to current climates, which has led many to conclude that this trait is evolutionarily constrained2-4. However, most studies have not accounted for the role of microclimates, potentially obscuring signals of local adaptation. We examined heat tolerance in 95 species of wild bees that varied in nesting behaviour across the latitudinal extent of Australia. Species nest (ground, wooden cavities, or plant stems) micro-climate temperatures predicted heat tolerance evolution, where stem nesters evolved the highest heat tolerances, and ground nesters evolved the lowest heat tolerances due to their ability to evade extreme heat. A moderate level of phylogenetic inertia in heat tolerance was explained by patterns of related species sharing nesting behaviours. This indicated repeated adaptive evolution of similar heat tolerances, rather than strong evolutionary constraints on heat tolerance. Finally, incorporating nesting behaviour into assessments of climate change vulnerability changed the rank order of which species were most at risk. This underscores the need to understand what drives the evolution of heat tolerance across species to better identify the taxa most at risk to climate change.

ecology↗

bioRxiv2024

Retention of the full visual opsin repertoire in Australia's cryptozoic lizards

Australian scincid lizards in the sister-genera Lerista and Ctenotus are a prominent system for understanding adaptation in the transition from surface to fossorial life. The approximately 205 species in this group exhibit extreme diversity in morphology and ecology. Lerista and Ctenotus both include diurnal and surface-active species that are fully pentadactyl, and Lerista also contains many specialised limb-reduced and limbless sand-swimmers. To understand how the visual systems of these lizards have responded to their varied photic environments, we examined the five opsin genes encoding the pigments that mediate colour and dim-light vision. These genes were sequenced for 59 species of Lerista and Ctenotus and analysed for variation in selection pressures among amino acid sites and across branches in the species tree. All five opsins are present and intact in all species of Lerista and Ctenotus examined, and we identified signals of positively selected substitutions in all five opsin genes -RH1, which mediates scotopic vision, and four cone opsins associated with photopic vision (SWS1, SWS2, RH2, LWS). Most comparisons of selection pressures did not show significant differences according to broad ecological divisions. Only LWS showed a signal of relaxed selection in sand-swimming (limb reduced) versus less fossorial (fully limbed) Lerista. These results suggest that photopic abilities are retained across both clades, even in the most fossorial species, highlighting a need for studies of visual ecology of Australian skinks, and prompts caution with regards to generalisations about degenerate vision in fossorial squamates.

molecular biology↗

bioRxiv2022

Assessing risk for butterflies in the context of climate change, demographic uncertainty, and heterogenous data sources

AbstractOngoing declines in insect populations have led to substantial concern and calls for conservation action. However, even for relatively well-studied groups, like butterflies, information relevant to species-specific status and risk is scattered across field guides, the scientific literature, and agency reports. Consequently, attention and resources have been spent on a miniscule fraction of insect diversity, including a few well-studied butterflies. Here we bring together heterogenous sources of information for 396 butterfly species to provide the first regional assessment of butterflies for the 11 western US states. For 184 species, we use monitoring data to characterize historical and projected trends in population abundance. For another 212 species (for which monitoring data are not available, but other types of information can be collected), we use exposure to climate change, development, geographic range, number of host plants, and other factors to rank species for conservation concern. A phylogenetic signal is apparent, with concentrations of declining and at-risk species in the families Lycaenidae and Hesperiidae. A geographic bias exists in that many species that lack monitoring data occur in more southern states where we expect that impacts of warming and drying trends will be most severe. Legal protection is rare among the taxa with the highest risk values: of the top 100 species, one is listed as threatened under the US Endangered Species Act and one is a candidate for listing. Among the many taxa not currently protected, we highlight a short list of species in decline, including Vanessa annabella, Thorybes mexicanus, Euchloe ausonides, and Pholisora catullus. Notably, many of these species have broad geographic ranges, which perhaps highlights a new era of insect conservation in which small or fragmented ranges will not be the only red flags that attract conservation attention.

ecology↗

bioRxiv2021

Gene flow between two thick-billed grasswren subspecies with low dispersal creates a genomic pattern of isolation-by-distance

ContextIn the era of the Anthropocene, habitat loss and environmental change threaten the persistence of many species. Genotyping-By-Sequencing (GBS) is a useful molecular tool for understanding how patterns of gene flow are associated with contemporary habitat distributions that may be affected by environmental change. Two parapatric subspecies of the threatened thick-billed grasswren (TBGW; Amytornis modestus) more frequently occur in different plant communities. As such, a preference for plant community type could reduce subspecific introgression and increase genetic diversity at the parapatric boundary. AimsWe aimed to measure gene flow within and among two TBGW subspecies and tested whether divergent genomic markers were associated with plant community type. MethodsWe sequenced 118 individuals from either of the two TBGW subspecies or in the region of parapatry and identified 7583 SNPs through ddRADseq. Key resultsWe found evidence of asymmetric gene flow and a genomic pattern of isolation-by-distance. There were sixteen genomic outliers correlated with plant community type (regardless of location). ConclusionsThese findings show that plant community type does not prevent introgression in one subspecies (A. m. raglessi), but low dispersal and habitat heterogeneity could contribute to the maintenance of distinct subspecific morphotypes. Local adaptation in different plant community types could also provide a mechanism for future divergence. ImplicationsWe suggest subspecific introgression could increase genetic variation and the adaptive potential of the species, facilitating species persistence under conditions of climate change. Introgression between grasswren subspeciesCharacterising gene flow facilitates conservation management. This study used genomic markers to measure gene flow between thick-billed grasswren subspecies and found results that support taxonomic identification of the two subspecies and suggests grasswrens have low dispersal and may benefit from increased genetic diversity. Recognition of models of divergence with gene flow will be necessary for future conservation management.

evolutionary biology↗