Biological Journal of the Linnean Society

Brain size and structure are hypothesized to be adaptively designed to satisfy the behavioral requirements of securing food and living socially. The importance of these socioecological and sociobiological selective forces in brain evolution is constantly debated. Socioecological divergence is striking in the Neotropical ant genus Neoponera: N. apicalis is a generalist solitary predator forming small colonies of ~100 whereas N. commutata colonies are approximately 10 times as large and workers pheromonally organize cooperatively raids only on Syntermes termite colonies. We interspecifically compared the size and structure of the compound eyes, size and number of antennal glomeruli, mosaic brain scaling and synaptic processing (microglomeruli-MG). Our results indicate that N. apicalis workers have a larger number of ommatidia, antennal lobe glomeruli, and allometrically larger antennal and optic lobes than N. commutata. These sensory traits were associated with differences in higher-order processing architectures in the mushroom body (MB) microglomeruli (MG). N. commutata workers had an allometrically larger MB, perhaps due to their socially complex chemical foraging communication, although MG density in N. apicalis was higher in both the MB lip and collar, regions associated with processing olfactory and visual information, respectively. The increase in MG density in N. apicalis may be associated with higher demands for navigation, learning, and memory, as well as a higher density of antennal lobe glomeruli to support prey odor discrimination. In contrast, N. commutata workers had larger ommatidia and antennal lobe glomeruli. Larger ommatidia correlate with their diurnal/nocturnal habits and a larger MB Our findings indicate that differences in behavioral performance demands associated with socioecological differentiation are reflected in variation in visual and olfactory system structure, brain size, mosaicism, and synaptic organization. Our results support both social and ecological brain hypothesis as drivers of mosaic brain evolution.

Reliable species delimitation underpins biodiversity assessment but remains difficult for organisms with plastic morphology and few diagnostic characters. Multispecies coalescent (MSC) methods can delimit species from genomic data, yet they are rarely tested in taxonomically complex, marine invertebrate groups where they are arguably most needed. We used the three Mediterranean species of the genus Tethya, a rare, well-characterised system within the otherwise taxonomically difficult phylum Porifera-distinguished by multiple independent morphological and ecological characters-to evaluate how robust MSC-based delimitation is in such groups. Analysing 64 single-copy nuclear loci in BEAST2 and BPP, we compared constrained, hypothesis-testing approaches (BFD*, BFdriver, A10) with freer, heuristic ones (SPEEDEMON, A11), and examined their sensitivity to data type, clock model, priors, and the species-collapse threshold. All methods recovered the three recognised Mediterranean species, but the resolution of within-lineage structure was method-dependent. The hypothesis-testing approaches consistently supported six lineages, robustly across data types and model assumptions, whereas the heuristic approaches proved less stable. Configurations without a priori species hypotheses often failed to converge or were computationally intractable, a problem compounded by the relaxed clock. In SPEEDEMON the outcome changed with the collapse threshold. Because our system lacks an independent reference point to calibrate this threshold, any delimitation based on it is poorly constrained. We conclude that constrained, hypothesis-testing delimitation is the most robust and reproducible MSC approach, yielding a quantitative, model-based hypothesis that can be weighed against other lines of evidence to inform taxonomic decisions. By clarifying how these methods behave and how their outcomes should be interpreted, our study offers a practical guide for researchers working on comparably complex systems.

For many group living species, vocal signals are a vital form of communication needed to coordinate social behaviours. Investigating these processes first requires a detailed description of the species vocal repertoire. White-nosed coatis (Nasua narica), which forage and move together in forest habitats, are thought to rely on vocalisations to coordinate movements and maintain group cohesion. However, quantitative studies of their vocal repertoire are lacking. We examined the vocal repertoire of white-nosed coatis from wild populations in Panama and Arizona, USA, to gain a more comprehensive view of their calling behaviours. By combining traditional acoustic analyses with an unsupervised approach based on spectrogram structure, we characterised the diversity of calls in this species and described the temporal and structural features of their vocalisations. We identified 19 call types, with some of these calls emitted in multi-syllable call sequences or in fast succession. We found variability in call rates among group members, which may be driven by differences in social status within the group. In addition, our results indicate that white-nosed coatis likely have individually-recognisable vocalisations. This study provides a foundational description of the white-nosed coati vocal repertoire, laying the groundwork for future research on vocal communication in this species.

The global study of freshwater clams in the genus Corbicula is frequently confounded by invasive androgenetic lineages that experience mitochondrial DNA capture and clonal propagation. In contrast, the endemic Corbicula of Sulawesi's ancient lakes reproduce sexually, offering a uniquely reliable system for mitochondrial population genetics. This study provides the first population-genetic framework for two endemic species, Corbicula possoensis (Lake Poso) and C. linduensis (Lake Lindu), using the cytochrome c oxidase subunit I (COI) marker. We analysed 90 newly generated COI sequences from C. possoensis (six stations) and C. linduensis (three stations), integrated with reference sequences from GenBank, to assess genetic diversity, population structure, and phylogeographic patterns. Hierarchical AMOVA revealed deep divergence between the two lakes ({Phi}_CT = 0.607), consistent with prolonged independent isolation rather than a single shared vicariance event, as the two species do not form a sister pair in the phylogeny. Within Lake Poso, C. possoensis exhibited exceptionally high genetic diversity (24 haplotypes; h = 0.876; {pi} = 0.016) and pronounced micro-geographic structuring into three phylogeographic zones (North: Tentena and Siuri; East: Tando Nceppo and Busogo Beach; Southwest: Bancea and Pendolo), each characterised by distinct haplogroups. Remarkably, the maximum divergence between zones (K2P = 2.33%) approached the interspecific distance between C. possoensis and C. linduensis (K2P = 2.42%), indicating that within-lake mitochondrial divergence has reached near-interspecific levels. Conversely, C. linduensis displayed near-panmixia and extreme genetic depauperation (3 haplotypes; h = 0.246; {pi} = 0.0004), indicating long-term demographic stasis within a restricted habitat. The deep phylogeographic zonation in C. possoensis suggests that its discrete populations should be treated as separate Management Units (MUs) in conservation planning to preserve locally adapted gene complexes, whereas the severely depauperate gene pool of C. linduensis renders it critically vulnerable to environmental disturbance and invasive species, warranting urgent IUCN Red List assessment. To validate these mitochondrial boundaries and inform future conservation strategies, multi-marker and genome-wide reassessments are strongly recommended.

The timing of reproductive processes can influence how mating interactions shape reproductive strategies. We examined how female age correlates with receptivity and preference in the jumping spider Habronattus formosus, a system characterized by elaborate male courtship and strong female choice. To test how receptivity changes across the post-maturation period, we paired females of different ages with males and quantified male courtship displays and mating outcomes. Females were not receptive immediately after maturation and instead exhibited receptivity primarily 2-3 weeks after maturation. We further found that the full male courtship predicted mating success in older females, whereas only the second stage of the courtship predicted success in younger females. The delay in female receptivity is consistent with expectations for strong female choice systems, where females may have a greater opportunity to evaluate male courtship before mating. These results highlight the importance of age-dependent changes in female reproductive state and suggest that the timing of receptivity may shape how different components of male courtship influence mating success.

The European flat oyster (Ostrea edulis), like numerous other oyster species, has been exploited for millennia and cultivated and translocated for centuries. Following a severe population decline, and in the context of ongoing conservation and restoration programs, genetic considerations must now be addressed to avoid mistakes. The objective of our study was to complement population genetic studies conducted at various scales along European coasts. Our sampling primarily targeted the French Atlantic, English Channel, and Mediterranean coasts, aiming to provide a fine-scale genetic characterization of populations in these regions. By integrating SNP array and low-coverage sequencing datasets, we obtained a comprehensive overview of the population genetic structure of Ostrea edulis across western Europe. Most previously identified clusters in Western Europe were confirmed. In France, populations assigned to these clusters exhibited notable within-patch homogeneity. However, two key findings emerged: (1) an extensive overlap zone between the Atlantic and western Mediterranean clusters, spanning at least from southern Portugal to southern France, and (2) the detection of a novel, clearly distinct cryptic cluster east of the English Channel, whose geographic range remains to be better delineated. These insights are critical for informing management decisions, particularly as restoration and conservation plans are currently being implemented across the species range.

Genomic offset (GO) is increasingly used to predict population maladaptation risk under climate change, with larger offsets assumed to indicate greater vulnerability. Despite rapid adoption in conservation planning, it remains unclear how sensitive GO estimates are to key methodological choices, including SNP set composition, genotype-environment association (GEA) methods, and the specific GO metric used. Empirical validation against observed population dynamics also remains limited. Here, we evaluate the methodological robustness and predictive performance of GO using multidecadal demographic monitoring data from Lycaeides butterflies, a system with short generation times and high fecundity that may facilitate rapid adaptive responses. GO estimates were broadly consistent across SNP sets, regardless of composition or size, with climate-associated and randomly selected SNPs yielding largely concordant values. Consistency across GEA methods was moderate and depended on the SNP set used. In contrast, GO metrics differed substantially in the magnitude of maladaptation estimated, suggesting they capture distinct biological signals and should not be treated as interchangeable. Crucially, GO was a poor predictor of observed population trends, regardless of SNP set composition, GO metric, or GEA method, both at sites used to fit GEA models and when extrapolated to independent demographic sites. These findings suggest that, while GO provides a valuable conceptual framework for assessing potential maladaptation, its quantitative estimates and predictive power are sensitive to methodological choices and species-specific biological context. We therefore urge careful alignment of GO metric assumptions with conservation objectives, along with rigorous empirical validation, before GO estimates are used to inform management decisions.

One challenge of reintroduction programs is ensuring that captive individuals are prepared for life in the wild, including having the ability to forage on wild resources. Foraging proficiency can be especially challenging to foster in species with a wide dietary breadth or reliance on ephemerally available resources. A relatively unexplored obstacle to release readiness may be an animals hesitancy to approach or consume unfamiliar foods, i.e. their neophobia and dietary conservatism. In this study, we examined the responses of a conservation breeding population of the extinct-in-the-wild alal[a] (Corvus hawaiiensis), a dietary generalist, to novel and familiar native and non-native fruits. Birds were similarly willing to contact both novel and familiar fruits, suggesting little aversion to the presence and appearance of novel food items. However, birds showed a clear preference for contacting non-native fruits over native fruits, regardless of familiarity. Additionally, while birds were willing to contact novel items, they were less likely to consume novel native fruits, suggesting that dietary conservatism may limit incorporation of these resources in the wild. Finally, juvenile birds were less likely to approach the testing setup and contact items, suggesting that neophobia may constrain their exploration of novel environments and resources. We discuss the implications of alal[a] preferences for non-native foods and reluctance to consume novel native items for pre-release preparations and the goal of wild species recovery.

Urban environments impose strong selective pressures through biotic and abiotic factors, driving changes in behavior, physiology, and morphology. Yet, responses vary across taxa and cities, and it remains unclear which traits respond consistently and what factors moderate this variation. We addressed these questions using the widespread European garden spider (Araneus diadematus) as a model, measuring size, color, and web-building traits along urban-rural transects in 22 cities across its distribution range. Using a meta-analytic framework, we assessed how city-specific characteristics influenced trait variation. Urbanization consistently reduced relative abdomen surface area, a proxy for body condition. Exploratory meta-regressions suggest that web-building response was predicted by temperature: compared to their non-urban surroundings, urban webs are larger in colder regions and smaller in warmer regions. In contrast, body size and abdomen brightness varied among cities without clear environmental predictors. These findings show that urbanization effects are trait- and context-dependent, likely influenced by local factors such as heat island intensity, microclimate, or prey availability. Linking within- and between-city variation will improve understanding of species phenotypic responses to urban environments.

In search of recurrent patterns of postzygotic hybrid incompatibility, we investigated the Holarctic 'Old World Swallowtail' (Papilio machaon Linnaeus) butterfly complex, whose members can easily be crossed in the laboratory. How many species this model system comprises remains unclear, as taxa with highly distinctive larvae but uncertain status come into contact with authentic P. machaon subspecies in Southern parts of the Palearctic region. By determining mitochondrial and ITS2 haplotypes within and away from contact zones, we found that these neighboring populations do exchange genes, as expected from F1 hybrids being generally fertile in our laboratory crosses. Nevertheless, recurrent instances of dysregulation of diapause were uncovered in hybrid progenies. In keeping with Haldane's Rule, pupae of the heterogametic (female) sex were either unable to enter diapause or, in reciprocal crosses, unable to resume development after having initiated diapause, whereas F1 males experienced normal, photoperiod-regulated diapause, but passed on abnormal diapause regulation to part of their female offspring when backcrossed. Comparing male and female pupal weights in hybrid progenies provides estimates of parental incompatibility that allow to rank taxa and predict quantitatively the outcome of additional crosses, as expected if the same regulatory system were involved. A survey of the entomological literature confirms that diapausing pupae that cannot resume development ('perpetual nymphs') are a recurrent feature of interspecific lepidopteran crosses. Moreover, of the two parent species of a perpetual nymph, the paternal one generally has fewer broods per year. These observations are discussed in the light of models of the speciation process.

Climate change can threaten population viability by disrupting sex ratios in species whose sex is influenced by temperature. While species with sex chromosomes were historically considered immune, in some species, temperatures can override genetic sex determination via sex reversal, leaving them vulnerable to climate-driven sex ratio shifts. The Tasmanian spotted snow skink (Carinacincus ocellatus), a viviparous reptile with an XX/XY system, provides a compelling case study. While laboratory studies demonstrated that extreme thermal conditions induce female-to-male sex reversal (XX males), its occurrence in the wild remains unexplored, limiting our understanding of actual climate impacts. Integrating 23 years of phenotypic and genetic sexing data across two climatically distinct populations, we provide the first evidence of sex reversal in a wild viviparous reptile. XX reversal occurred in both populations, affecting up to 23.5% of XX births in the warmer population, and was associated with colder minimum daily temperatures. Despite high birth rates in some years, sex-reversed adults were rare. We also identified putative XY females, suggesting bidirectional sex reversal and reinforcing the extreme plasticity of reptilian sex determination. Ultimately, sex reversal could act as an evolutionary trap, potentially compromising population viability as climate instability increases.

The origin of novel phenotypes can influence access to new ecological resources, which may have positive, neutral, or negative effects on subsequent phenotypic diversification. In this study, we tested the macroevolutionary consequences of a pair of putative functional innovations occurring in deep-sea fishes of the order Stomiiformes. Integrating phylogenetic comparative methods, micro-CT scans, and external body measurements, we recover a mosaic of diversification trends associated with these innovations. We found some evidence for elevated evolutionary rates in tooth morphology associated with the predatory dragonfishes, which possess a gap between their vertebral column and skull that exposes the notochord and enables neck-like flexibility. However, a second novelty building upon the first, a functional neck joint enabling extreme cranial kinesis, was linked to faster rates of skull evolution. Our results suggest that innovations that help shift ecological roles and overcome functional constraints related to those roles, like gape-limitation in prey depauperate habitats, may play an important role in promoting phenotypic diversification. This work builds on a growing body of evidence highlighting how the deep sea promotes phenotypic diversity, generating the extreme forms that are celebrated by scientists and the public alike.

This study presents a systematic revision of the suborder Astrophorina for the temperate Pacific coast of the United States and Canada. Major findings include a reduction in the number of species previously thought to range into the region from Japan; validation of most Geodia species erected by Lendenfeld (1910), which were later synonymized by de Laubenfels (1932); the formal description of 10 new species (Poecillastra alaskensis sp. nov., Vulcanella explorata sp. nov., Vulcanella rupta sp. nov., Stelletta cardenasi sp. nov., Stelletta nicolenya sp. nov., Stelletta limuwensis sp. nov., Dercitus (Stoeba) giveni sp. nov., Penares anyapax sp. nov., Penares foxi sp. nov., and Thenea diastra sp. nov.); and one new combination, Penares orientalis comb. nov. Extensive SCUBA-based collection efforts yielded new samples for 11 of the 26 species identified in the region, which enabled an integrative taxonomic approach that combined field photography, fresh material for DNA sequencing, and improved characterization of species ranges and morphological variability in previously described taxa. Illumina sequencing generated complete nuclear ribosomal haplotypes for five species, while Sanger sequencing of the 28S and cox1 loci placed 20 of the 26 species within molecular phylogenies. The use of very short "mini-barcode" amplicons also enabled sequence recovery from historic type specimens up to 137 years old. This study additionally reports the discovery of sponge grounds of abundant, large Geodia at diving depths in Southern California. Together, these results substantially advance our understanding of global astrophorid diversity and systematics, and the biogeography of sponge diversity in the Northeast Pacific. Note about species names: this pre-print is not intended to be a publication of the associated species names for the purposes of zoological nomenclature.

1. Detecting environmental DNA (eDNA) from rare or low-abundance aquatic species remains a major challenge, particularly when it is highly degraded, present at low concentrations, and dominated by DNA from non-target taxa. These challenges are further amplified in sedimentary ancient DNA (sedaDNA) studies, where thousands of years can degrade eDNA further, making the detection and quantitative interpretation of weak biological signals difficult. 2. Metabarcoding is commonly used to produce high-throughput community-level data from eDNA but is inherently compositional and influenced by amplification biases. Nonetheless, metabarcoding read abundance or PCR replicate detection frequency are increasingly used as proxies for relative DNA concentration, but their quantitative interpretation has rarely been evaluated against independent measures of absolute DNA abundance. 3. We used droplet digital PCR (ddPCR) to quantify mitochondrial DNA from Atlantic cod (Gadus morhua) and Atlantic herring (Clupea harengus) in 136 ancient eDNA extracts from Icelandic marine sediment cores spanning the last three millennia. We compared ddPCR copy number estimates with metabarcoding (18S) derived relative abundance and detection frequency, and evaluated whether temporal DNA trends corresponded with proxy reconstructed sea surface temperature (SST) variability. 4. We found that ddPCR-measured fish sedaDNA abundance was positively correlated with the proportion of metabarcoding PCR replicates for both Atlantic cod and Atlantic herring. Moreover, temporal trends in Atlantic herring DNA abundance were consistent with proxy reconstructed SST variability, supporting the ecological relevance of the molecular signal. 5. Overall, our results show that ddPCR-derived DNA concentrations and metabarcoding PCR replicate detection frequency capture consistent patterns in low-abundance fish sedaDNA from marine sediments. The observed agreement between approaches supports the use of PCR replicate detection frequency as a semi-quantitative proxy for low-abundance sedaDNA.

In many insect species, mating is coordinated through multimodal signaling, yet less obvious channels are often overlooked. In the burying beetle Nicrophorus vespilloides, chemical communication is well-documented, but the role of substrate-borne vibrational signals (stridulations) during courtship remains unknown. We investigated whether stridulation is essential for mating success through two sets of experiments. First, we found a positive correlation between the frequency of stridulations and both the number and duration of copulation events. Second, we employed a silencing experiment to test the necessity of these signals by silencing males, females, or both partners. We found no significant differences between silenced and control groups regarding the frequency or duration of physical contact and mounting events, suggesting that stridulation is not required for mate recognition or the initiation of courtship. However, the proportion of successful copulations relative to mounting events was significantly lower when females were silenced. These results suggest that while N. vespilloides relies on a redundant multimodal system that likely utilizes chemical cues to initiate mating, vibrational signals, particularly from the female, may play a critical role in facilitating successful copulation. This study provides the first evidence for the role of stridulation in the mating behavior of N. vespilloides and highlights the potential for female-mediated vibrational signaling in burying beetle courtship.

To make adaptive foraging decisions, naive individuals need to gather information about the local prey community. Besides sampling prey personally, the young could gather information about prey profitability by observing the foraging behaviour of other individuals, and parental provisioning provides the first opportunity to acquire this social information. Still, previous research on vertical transmission of prey preferences from parents has provided mixed results that are often confounded with other information sources, such as siblings and peers. It is also not known whether information from parents can change potential innate biases against certain prey types, such as avoidance of warningly coloured insects. Here, we tested whether social information acquired by offspring during parental provisioning influences the development of prey preferences in a generalist predator, the Great Tit (Parus major). We brought 15 great tit broods and their parents into captivity at late nestling stage (14 days old) and divided them into three social information treatments where parents were provided with either brown, red or yellow palatable maggots to feed to their dependent young for 8 days. Once foraging independently from parents, we conducted a preference test where juveniles were offered the full array of coloured maggots. Regardless of palatable exposure to typical warning-coloured maggots (i.e. red and yellow), juveniles consistently preferred yellow over red, and preferred brown maggots the most (i.e. lacking warning coloration). This supports the existence of innate biases against typical warning colours, and that social information from parents is unlikely to override these, at least when alternative prey is easily available.

In over a thousand avian species, pairs coordinate vocalizations to form duets. Songbirds may use calls (simple, non-learned vocalizations) and songs (complex, learned vocalizations) to answer their partners. In Galapagos Yellow Warblers (Setophaga petechia aureola), song answers in duets appear to have evolved recently in addition to older call answers. Here, we explored the structure and functions of duets in an observational study to understand why song answers in duets may have evolved. We first described the temporal structure of duets initiated by either sex. We then tested whether the distance between pair members, countersinging with neighbours, and timing relative to aggressive encounters predicted answering probability for each sex. Finally, we tested whether the behavioral context of call and song answers differed. We found that most duets were initiated by males, and call answers were almost exclusively given by females. Female answers were also more tightly coordinated than those of males. Female answering probability decreased with increasing distance between pair members, whereas male answering probability did not. In addition, females were less likely to answer with songs when farther from their mate. Females answering probability also increased slightly when their mates initiation was preceded by a neighbors song. Our results show some evidence in support of the joint resource defence hypothesis for female answers. On the other hand, the significance of song in female answers may be related to some other functions that we did not test here, such as signaling quality or commitment to the pair bond. Lay summaryWho turns a song into a duet? In Galapagos Yellow Warblers, it is usually the female: she answers her mates song with a tightly timed call or song. Male replies were rarer and less coordinated. While male replies didnt seem to have a function, female replies were used in territorial disputes with neighbours and may indicate joint ownership of a territory. Female song replies, on the other hand, may signal commitment to the pair bond.

Animals fight for resources to obtain fitness benefits; most contests are intrasexual, and males tend to fight more than females. Although the genetic basis of male aggression is well studied, we know little about the genetic variation of female aggression. Female aggression varies with reproductive status and is potentially influenced not only by her genotype, but also by the genotype of her mate. Here we measured both male and female aggression in a set of Drosophila melanogaster inbred lines by competing each line against a standard competitor. Aggression varied among lines for both sexes, but male and female aggression were not correlated. Female aggression for many lines increased with mating, as expected, but not all lines changed aggression. However, when females were mated to males of different lines, male genotype did not affect the post-mating change in aggression, suggesting that ejaculate-mediated effects do not vary across these lines. The aggression level of the standard opponent was positively correlated with that of focal individuals indicating that individuals modulate their behavior according to the genotype of their opponent.

The general random walk model (GRW) of Hunt (2006) is used to infer directional evolution in mean trait values from sparse fossil data by modeling phenotypic change as the accumulated result of small steps with mean step sizes and step variances. Using simulations and real data cases, Ergon (2026) showed that the step variances can be estimated reasonably well only when the mean trait values have small measurement errors, while for fossil data with realistic measurement errors they appear to be extremely difficult to find, and they are often found to be negative. In the simulations Ergon (2026) assumed that the true phenotypic mean values were known. Here, I essentially repeat these simulations under the assumption that only mean trait values with large measurement errors are known, and based on weighted mean squared error (WMSE) comparisons the conclusion is that weighted least squares (WLS) is a better method than GRW. A second conclusion is that WLS is a better method also in the possibly rare cases with large measurement errors where the GRW parameters are estimated well. The GRW method is simply not flexible enough to handle such cases. A third conclusion is that Akaike Information Criterion (AIC) results for GRW models with large measurement errors relative to the step variance may be overly optimistic.

Biological invasions on islands provide a natural framework to study how dispersal and connectivity influence evolutionary and ecological processes. The avian nest parasitic fly, Philornis downsi - first recorded in Darwin's finch nests in 1997 - causes high mortality in endemic land birds, yet its inter-island and sex-specific patterns of dispersal and genetic structure remain poorly understood. We use low-coverage whole genome sequencing to investigate genome-wide patterns of genetic diversity, directional migration and effective population size in P. downsi across five major Galapagos Islands and its native range in mainland Ecuador. We find evidence for a genetic bottleneck in the Galapagos, isolation by distance, and evidence that the island closest to the Ecuadorian mainland, San Cristobal, is genetically divergent from the other four islands sampled, despite retaining the highest genetic diversity. No evidence was found for sex-biased dispersal; however, sex-biased genetic structure was detected using only markers from inferred autosomal scaffolds. We found asymmetric gene flow with higher migration rates from San Cristobal westward to the other islands, matching the direction of both southeast trade winds and major cargo shipping routes. Our results suggest both natural and human-mediated colonisation of P. downsi from the mainland through San Cristobal to the other islands, followed by high inter-island dispersal among closely situated sink islands. Our findings are critical for prioritising islands for control strategies that will reduce P. downsi impacts on vulnerable endemic birds and underscore the value of understanding directional migration patterns for managing invasive species in metapopulations.