Biology subjects

Amundsen, T.

Publications and source records attributed to Amundsen, T..

3 recordsLinked to original sources

bioRxiv2026

Female-biased sex ratios despite stable genetic sex determination across a climatic gradient in a marine fish

Adult sex ratio (ASR) is a fundamental parameter shaping population dynamics and evolutionary trajectories. In theory, ASR is governed by the sex determination (SD) system and sex-specific mortality. Yet, ASR is often hard to predict in natural populations because of ecological effects on its determinants. We address this ecological complexity by investigating the drivers of ASR across a steep climatic gradient in Scandinavian populations of the two-spotted goby Pomatoschistus flavescens. Demographic surveys accounting for over 25000 fish in 30 locations, spanning 10{degrees} of latitude, revealed a general female-bias of the ASR, ca. 75%. To assess the contribution of SD, we combined reduced representation sequencing of 180 adults with our novel long-read male genome assembly. We characterised the genetic architecture of an XX/XY SD system, and identified a male-specific duplicate from the TGF-{beta} signaling pathway, amhr2y, as a candidate sex-determining gene. Subsequent genotyping of eggs and juveniles showed consistently unbiased sex ratios across latitudes, implying that the female-biased arises at later life stages. Interpreted in the light of historical data, our findings allow us to reject environmental sex determination and sex-biased mortality as important drivers of ASR bias in this species. We propose instead that the female bias originates from sex-specific patterns of habitat distribution, which could result from ecological conditions interacting with the distinct reproductive strategies of females and males. Our results underscore the need to go beyond primary theoretical expectations to understand fundamental demographic parameters within their relevant ecological context.

evolutionary biology↗

bioRxiv2026

Local mating competition, but not climate, drives male reproductive success across a latitudinal gradient in a nest-brooding marine fish

Understanding ecological drivers of reproductive success is crucial to predict whether natural populations can cope with the pace of anthropogenically driven environmental change. In marine ecosystems, this knowledge is difficult to acquire due to the lack of tractable field systems. Here, we took advantage of the nest-brooding behavior of the two-spotted goby Pomatoschistus flavescens, an important planktivorous fish in Scandinavian coastal ecosystems, to study its reproduction across the steep climatic gradient of its natural range. We deployed 360 artificial nests in the field, covering six populations during the breeding season of 2022. We found that climate explained differences among populations in the phenotypes of nest-holding males, and in the impact of both marine growth and parental cannibalism on the broods. In addition, climate affected egg density and diameter. Despite these ecological effects, and although populations differed in average male reproductive success, reproductive success was not influenced by climate. Instead, it was largely determined by competition occurring at the local scale, in particular through the acquisition of high-quality nests, which was itself affected by the relative size of males within the local pool. We propose that the frequency-dependent nature of mating competition may buffer reproductive success against climatic influence in P. flavescens, and discuss the potential generality of such mechanisms and implications for population resilience.

evolutionary biology↗

bioRxiv2024

Sexual display behavior follows consistent sex-specific reaction norms across latitude in response to operational sex-ratio.

Predicting the strength and direction of sexual selection is a challenging task for evolutionary theory, as the effects of ecological factors, social environment, and behavioural plasticity, all need to be taken into account. The Operational Sex Ratio (OSR) is a key variable, which has been shown to (i) affect the strength and direction of mating competition, as a social environment cue, and (ii) be affected itself by ecological conditions through sex-specific environmental effects. Yet, gaining a global view of (i) and (ii) in wild populations represents an arduous but necessary step to further our understanding of sexual selection dynamics in the wild. Here, we address this challenge by using reaction norms. We conducted an extensive field study on the two-spotted goby Pomatoschistus flavescens, monitoring six populations along a latitudinal gradient during an entire breeding season. Doing so, we compared across populations the temporal trajectories in social environment and sexual displays, which is unprecedented. We develop a reaction norm framework based on OSR theory to analyse the data. We show that what appears to be tremendous variation in sexual displays across populations and sampling times, follows consistent rules: sexual display behaviour follows behavioural reaction norms in response to the social environment that are consistent across populations, but social environment fluctuations are specific to each population. Recording behaviour not only over time, but also along a latitudinal gradient where ecological conditions change and in turn affect OSR, was necessary to gain insight into the relationship between social environment and sexual displays, which in turn contributes to sexual selection dynamics.

evolutionary biology↗