Biology subjects

Sendell-Price, A. T.

Publications and source records attributed to Sendell-Price, A. T..

7 recordsLinked to original sources

bioRxiv2026

Recent hybridisation and ghost introgression among a trio of island passerines

Hybridisation between species was once considered a relatively uncommon occurrence but is now recognised to occur frequently across many different taxa. It can result in homogenisation of previously distinct forms, a potential conservation issue, but can also act as a catalyst for diversification through introgression and sharing of favourable genes. Repeated rounds of island colonisation followed by speciation result in secondary sympatry, with the potential for hybridisation between early and late arrivers. In the southwest Pacific, this situation has arisen in the avian family Zosteropidae (the white-eyes). Here we use whole genome sequencing of live birds and historical specimens to characterise hybridisation between three white-eye species on Norfolk Island: two island endemics, Zosterops tenuirostris and the now-extinct Zosterops albogularis, and Zosterops lateralis, which colonised the island in 1904. Despite over two million years of divergence between Z. lateralis and the two endemics, we provide genomic evidence of their hybridisation. First, we confirm the identities of three Z. lateralis x Z. tenuirostris hybrids and additionally identify one Z. lateralis x Z. albogularis hybrid. We also report asymmetric, genome-wide introgression from both endemics into Z. lateralis, with introgressed regions enriched for a range of potential functions. However, despite this introgression, species boundaries have been maintained, and the extant endemic Z. tenuirostris does not appear to be at risk of genetic extinction. Our work additionally demonstrates an unusual case of recent ghost introgression from the extinct Z. albogularis into Z. lateralis. This study sheds light on the genomic outcomes of secondary sympatry and its potential consequences for single-island endemics.

evolutionary biology↗

bioRxiv2024

Islands promote diversification within the silvereye clade: a phylogenomic analysis of a great speciator

Geographic isolation plays a pivotal role in speciation by restricting gene flow between populations through distance or physical barriers. However, the speciation process is complex, influenced by the interplay between dispersal ability and geographic isolation, especially in "great speciators" - bird species present on multiple islands that, at the same time, have many subspecies. Comparing population differentiation in both continental and insular settings can help us to understand the importance of geographical context in the emergence of great speciators. The highly diverse white-eye family Zosteropidae includes several great speciators, including the silvereye (Zosterops lateralis) which consists of 16 subspecies, 11 occurring on islands. The distribution of the silvereye on the Australian continent and numerous southwest Pacific islands allows us to explore the influence of different forms of geographic isolation on population divergence. To do this, we conducted a comprehensive phylogenomic analysis of the silvereye and compared patterns of population divergence in insular versus continental silvereye populations. We estimate that the silvereye lineage emerged approximately 1.5 million years ago, followed by the split of the two main silvereye clades: Southern Melanesia and the broader South Pacific (encompassing Australia, New Zealand, and outlying islands). Continental populations show low genetic population structure, which suggests that they can overcome multiple forms of geographic barriers across long distances. In contrast, most island populations are highly structured even over relatively short distances. Divergence statistics further support the idea that water barriers lead to a higher population differentiation when compared to continental distances. Our results indicate that islands promote divergence and provide an empirical example of the geographical conditions that result in the emergence of great speciators.

evolutionary biology↗

bioRxiv2023

Standing genetic variation and de novo mutations underlie parallel evolution of island bird phenotypes

Parallel evolution occurs when the same trait evolves in closely related lineages in response to similar ecological contexts and provides some of the best examples of determinism in evolutionary biology. However, from a genetic standpoint, this process can be driven by either new mutations that appear independently in each diverging population or by selection on existing genetic variation common to both lineages. Small-bodied birds, for example, tend to increase in size after they colonise a new island, following what is known as the island rule. Such is the case of the silvereye (Zosterops lateralis), a prolific natural coloniser of southwest Pacific islands. Island forms of this bird species increase in body size after they establish, with the pattern and pace of change consistent with directional natural selection and evident even in the most recent colonisations within the last 200 years. The system provides an exceptional opportunity to explore the genomic basis of repeated body size evolution. We sequenced 377 whole genomes from 31 different silvereye populations, which revealed that both mechanisms are at play: in some lineages, new mutations are highly associated with body and bill size, but there are also highly associated polymorphisms present across all populations. Our research sheds light on the genomic basis of repeated body size evolution and emphasises that multiple molecular mechanisms can underlie similar evolutionary trajectories even within a single taxon.

evolutionary biology↗

bioRxiv2023

Candidate gene length polymorphisms are linked to dispersive behaviour: searching for a mechanism behind the "paradox of the great speciators"

The "paradox of the great speciators" has puzzled evolutionary biologists for over half a century. A great speciator requires excellent dispersal ability to explain its occurrence on multiple islands, but reduced dispersal ability to explain its high number of subspecies. A rapid reduction in dispersal ability is often invoked to solve this apparent paradox, but a proximate mechanism has not been identified. Here, we explore the role of six genes linked to migration and animal personality differences (CREB1, CLOCK, ADCYAP1, NPAS2, DRD4, and SERT) in 20 South Pacific populations of silvereye (Zosterops lateralis) that range from highly sedentary to partially migratory, to determine if genetic variation is associated with dispersal propensity. We detected genetic associations in three of the six genes: i) in a partial migrant population, migrant individuals had longer microsatellite alleles at the CLOCK gene compared to resident individuals from the same population; ii) CREB1 displayed longer average microsatellite allele lengths in recently colonised island populations (< 200 years), compared to evolutionarily older populations. Bayesian broken stick regression models supported a reduction in CREB1 length with time since colonisation and decreasing dispersal propensity; and iii) like CREB1, DRD4 showed differences in polymorphisms between recent and old colonisations but a further sample size is needed to confirm. ADCYAP1, SERT, and NPAS2 were variable but that variation was not associated with dispersal propensity. The association of genetic variants at three genes with migration and dispersal ability in silvereyes provides the impetus for further exploration of genetic mechanisms underlying dispersal shifts, and the prospect of resolving a long-running evolutionary paradox through a genetic lens.

evolutionary biology↗

bioRxiv2022

Large effect loci have a prominent role in Darwin's finch evolution

A fundamental goal in evolutionary biology is to understand the genetic architecture of adaptive traits and its evolutionary relevance. Using whole-genome data of 3,958 Darwins finches on the Galapagos Island of Daphne Major we identify six loci of large effect that explain 46% of the variation in beak size of Geospiza fortis, a key ecological trait. Allele frequency changes across 30 years at these loci affected beak morphology in two ways. An abrupt change in beak size occurred in Geospiza fortis as a result of natural selection associated with a drought, and a more gradual change occurred in G. scandens as a result of introgressive hybridization. This study demonstrates how large effect loci are a major contributor to the genetic architecture of rapid diversification during adaptive radiations. One Sentence SummaryAllele frequency change at six loci of large effect causes evolutionary change in key ecological traits.

evolutionary biology↗

bioRxiv2020

The genomic landscape of divergence across the speciation continuum in island-colonising silvereyes (Zosterops lateralis)

A goal of the genomic era is to infer the evolutionary dynamics at play during the process of speciation by analysing the genomic landscape of divergence. However, empirical assessments of genomic landscapes under varying evolutionary scenarios are few, limiting the ability to achieve this goal. Here we combine RAD-sequencing and individual-based simulations to evaluate the genomic landscape in the silvereye (Zosterops lateralis). Using comparisons matched for divergence timeframe and gene flow context, we document how genomic patterns accumulate along the speciation continuum. In contrast to previous predictions, our results provide limited support for the idea that divergence accumulates around loci under divergent selection or that genomic islands widen with time. While a small number of genomic islands were found in populations diverging with and without gene flow, in few cases were SNPs putatively under selection tightly associated with genomic islands. Furthermore, we modelled the transition from localised to genome-wide levels of divergence using individual-based simulations that considered only neutral processes. Our results challenge the ubiquity of existing verbal models that explain the accumulation of genomic differences across the speciation continuum and instead support the idea that divergence both within and outside of genomic islands is important during the speciation process. DATA ACCESSION NUMBERSResequencing data from this study have been submitted to the National Center for Biotechnology Information (NCBI; https://www.ncbi.nlm.nih.gov) under accession number PRJNA489169.

evolutionary biology↗

bioRxiv2019

The multiple population genetic and demographic routes to islands of genomic divergence

1. The way that organisms diverge into reproductively isolated species is a major question in biology. The recent accumulation of genomic data provides promising opportunities to understand the genomic landscape of divergence, which describes the distribution of differences across genomes. Genomic areas of unusually high differentiation have been called genomic islands of divergence. Their formation has been attributed to a variety of mechanisms, but a prominent hypothesis is that they result from divergent selection over a small portion of the genome, with surrounding areas homogenised by gene flow. Such islands have often been interpreted as being associated with divergence with gene flow. However other mechanisms related to genetic architecture and population history can also contribute to the formation of genomic islands of divergence.\n\n2. We currently lack a quantitative framework to examine the dynamics of genomic landscapes under the complex and nuanced conditions that are found in natural systems. Here, we develop an individual-based simulation to explore the dynamics of diverging genomes under various scenarios of gene flow, selection and genotype-phenotype maps.\n\n3. Our modelling results are consistent with empirical observations demonstrating the formation of genomic islands under genetic isolation. Importantly, we have quantified the range of conditions that produce genomic islands. We demonstrate that the initial level of genetic diversity, drift, time since divergence, linkage disequilibrium, strength of selection and gene flow are all important factors that can influence the formation of genomic islands. Because the accumulation of genomic differentiation over time tends to erode the signal of genomic islands, genomic islands are more likely to be observed in recently divergent taxa, although not all recently diverged taxa will necessarily exhibit islands of genomic divergence. Gene flow primarily slows the swamping of islands of divergence with time.\n\n4. By using this framework, further studies may explore the relative influence of particular suites of events that contribute to the emergence of genomic islands under sympatric, parapatric and allopatric conditions. This approach represents a novel tool to explore quantitative expectations of the speciation process, and should prove useful in elucidating past and projecting future genomic evolution of any taxa.

genomics↗