Sex differences in social aggression are widespread across the animal kingdom, with males typically displaying greater territoriality. While this dimorphism has traditionally been attributed to sex hormones, sex chromosomes can also contribute to it independently of hormonal influence. In the African pygmy mouse Mus minutoides, naturally occurring sex-reversed XY females (named X*Y due to a mutation on the X chromosome) are highly territorial in comparison to the other female genotypes present in the population (XX and XX*). However, the molecular basis of this phenotype remains unknown. Here, we evaluate molecular factors, known to correlate with aggressiveness, following a standardized behavioural assessment of aggression. We focus on i) the androgen pathway by quantifying testosterone serum levels and expression of its receptor in the brain; ii) the brain dopaminergic system through expression of dopamine-regulating genes, including the sex-determining Sry gene; and iii) neuroendocrine circuits, via vasopressin and oxytocin expression. These systems, although distinct, converge on hypothalamic-limbic circuits that regulate social behaviour and threat responses, providing an integrated framework for the modulation of aggression. Contrary to earlier reports, we found reduced level of aggression in X*Y females, likely to reflect a breeding facility effect. We also observe no correlations between aggressiveness and androgen levels or gene expression of the tested factors. However, our results support a stimulation of the dopaminergic system and of the oxytocin pathway following the agonistic assay suggesting their potential involvement in aggression-related responses. This further supports the idea that aggression is multifactorial. It is shaped by the interaction of several neuroendocrine and neurotransmitter pathways rather than a single determinant. ### Competing Interest Statement The authors have declared no competing interest. Agence Nationale de la Recherche, https://ror.org/00rbzpz17, SEXREV no. 18‐CE02‐0018‐01
Adaptive introgression, the transfer of beneficial alleles between species through hybridization, is increasingly recognized as an important source of adaptation to novel environments. However, the theory of adaptive introgression has primarily been developed for a single panmictic population, whereas many empirical examples involve spatially subdivided populations. In such systems, a low-frequency adaptive allele may either represent the leading edge of an adaptive travelling wave or occur in a subpopulation where the introgressed allele is locally selected against. We developed a simple prediction based on the relationship between adaptive allele frequency and introgressed tract length. Simulations predict a positive correlation during an ongoing sweep of an unconditionally beneficial allele, but no correlation under local adaptation. Tract erosion provides a recombination clock for time since introgression, which also determines the distance travelled by the adaptive wave and hence allele frequency in the former, whereas allele frequency is determined by local selection in the latter. We tested this prediction in a well-characterized case of adaptive introgression, in the sea squirt Ciona intestinalis , using haplotagging to reconstruct phased genomes and local ancestry. We found no relationship between adaptive allele frequency and introgressed tract length, providing additional support for a model of local adaptation rather than ongoing global selective sweep. Author summary Hybridization between species can transfer beneficial genetic variants from one species to another, enabling the latter to adapt to a new environment. However, such variants are not necessarily advantageous throughout the recipient species range. In geographically subdivided populations, a low-frequency introgressed allele may either have arrived recently or be selected against locally. Using simulations, we show that combining allele frequency with introgressed tract lengths clarifies this ambiguity, offering a straightforward method to distinguish between globally positive and locally varying selection. When an adaptive allele is beneficial everywhere, it spreads through populations as a travelling wave. Over time, recombination progressively shortens introgressed tracts. Populations reached first have higher frequencies of the adaptive allele on longer introgressed tracts, whereas recently reached populations have lower frequencies on shorter tracts. When selection varies among populations, this relationship disappears because allele frequency reflects local selection rather than the history of the adaptive wave. We tested this prediction in a confirmed case of adaptive introgression in a sea squirt species by reconstructing ancestry along chromosomes and measuring introgressed tract lengths. We found no correlation between allele frequency and introgressed tract length, supporting the hypothesis that variation in introgressed allele frequency reflects local selection rather than a traveling adaptive wave. ### Competing Interest Statement The authors have declared no competing interest.
The diversity of ecological interactions, both trophic and non-trophic, is central to understanding the assembly of communities. However, we have yet to study non-trophic processes through their action on ecosystem compartments such as detritus involved in both recycling and habitat provisioning. Here, we study a simple ecosystem model where the dual role of detritus as both resource and habitat allows us to define ecosystem engineering from non-trophic processes that interact with the cycling of matter at the ecosystem level. Our results show how habitat and resource limitations on consumer growth from detritus can affect ecosystem stability. We further predict that non-trophic processes can stabilize ecosystems via 1) asynchrony between trophic and non-trophic interactions, 2) weak trophic interactions emerging from non-trophic feedbacks, and 3) coupling between non-trophic and recycling processes that control top-down versus bottom-up trophic regulation. Our results show that ecosystem dynamics provide the relevant context to study the interplay between trophic and non-trophic processes.
Heterogeneous genomic landscapes of differentiation can reveal evolutionary processes acting over different timescales. Whereas genetic structure in the European flat oyster, Ostrea edulis , is mainly shaped by geography, previous work suggested parallel differentiation between western and eastern Mediterranean populations and between Atlantic and North Sea populations, resulting in genetic convergence between range margin populations in some genomic regions. Here, we analyzed 27 oysters from four locations using moderate-coverage (∼20X) short-read whole-genome sequencing. We first examined three known chromosomal inversions and found evidence that they predate divergence with the sister species O. chilensis . We then scanned the genome for parallel differentiation at the individual-SNP rather than sliding-window scale using the product of allele-frequency differences across the two geographic contrasts. Two of the three inversions were detected, but we also identified 12 small non-inverted genomic regions showing even stronger signals of parallel differentiation. These “islands of parallelism” typically overlap one or a few genes, and most showed elevated dXY consistent with long-term barriers to gene flow. Two islands overlap nuclear ATP synthase subunits, while mitochondrial ATP8 shows a convergent amino-acid change, suggesting possible nuclear–nuclear and mitonuclear incompatibilities. Finally, demographic inference with heterogeneous gene flow supported post-glacial secondary contact and a lineage-based rather than geography-based population topology. Our results suggest that the genomes of O. edulis lineages have been largely porous to gene flow upon secondary contact, except for chromosomal inversions and small genomic islands. These regions likely act as barrier loci, preserving a signal of a shared evolutionary history among marginal populations that has otherwise been erased by rampant gene flow. ### Competing Interest Statement The authors have declared no competing interest.
Prospero-related homeobox (Prox) genes encode a family of transcription factors that play essential roles in the development of several organs and systems, including the central nervous system, lymphatic endothelium, musculature, and liver. Despite their developmental importance, the evolutionary history of the vertebrate Prox gene family remains poorly understood. In this study we combined phylogenetic and synteny analysis to characterise the evolution of the Prox family in vertebrates. Our results reveal that two to three Prox subfamilies were already present in the last common ancestor of jawed vertebrates. We clarify the identity and evolutionary relationships of well-studied members of this family and identify multiple independent losses of Prox2 and Prox3 genes in specific vertebrate lineages. Furthermore, we uncover evidence for the existence of a fourth Prox gene in the ancestral vertebrate genome, which was subsequently lost. Overall, this study provides the first comprehensive analysis of the evolutionary history of the vertebrate Prox gene family and establishes a foundations for future studies on the functional roles of these genes. ### Competing Interest Statement The authors have declared no competing interest. Swedish Research Council, https://ror.org/03zttf063, 2023-06503, 2022-04988 Magnus Bergvalls Stiftelse, https://ror.org/040ya8k73, 2024-1281, 2022-441 Carl Tryggers stiftelse för vetenskaplig forskning, https://ror.org/048p4fn82, CTS22-1949, CTS24-3873
