Biomedical subjects

Andrew P Hendry

Publications and source records attributed to Andrew P Hendry.

3 recordsLinked to original sources

PubMed2026

The Spatial and Temporal Repeatability of Genomic Responses to Natural Selection as Demonstrated in Stickleback Populations Experiencing Highly Dynamic Environments.

The evolution of genotypic parallelism under shared environmental conditions provides strong evidence for the role of natural selection. However, analyses typically examine genomic signatures of selection long after the putative selection event and only assess the repeatability of responses across spatial population replicates. This impedes our ability to attribute a particular response to a given selection pressure and to distinguish non-parallel responses caused by stochastic processes from those caused by local selection. As such, the consistency of natural selection over space and time is unknown, and the role of persistent local selection pressures is unclear. Here, we leveraged the natural bar-built estuary system of Santa Cruz, California, to examine the repeatability of seasonal genomic change in threespine stickleback (Gasterosteus aculeatus) over space and time. By comparing allele-frequency shifts that are shared across locations (spatial repeatability) with those that are shared across years within locations (temporal repeatability), we identified both spatially shared and local components of putative selection. We found that repeated seasonal outlier responses occurred more often than expected under a neutral null model. Although repeatability declined as the number of estuaries sharing an outlier increased, enrichment above neutral expectations increased with broader spatial sharing, particularly for outliers repeated across both years. While the precise outlier SNPs varied across years, estuary-specific patterns of responses were broadly consistent, suggesting an important role for local conditions. Together, our findings show that temporal sampling can reveal components of putative selection that would be missed from spatial comparisons alone. More broadly, they highlight the importance of examining repeatability over both space and time to understand the parallel and non-parallel components of adaptive genomic change.

Animals↗

PubMed2002

Egg-size evolution in aquatic environments: does oxygen availability constrain size?

Selection against large eggs has been proposed for aquatic environments, putatively because large eggs should have more difficulty obtaining the required oxygen. Here, we use brown trout (Salmo trutta) eggs to provide an experimental test of this hypothesis. At high levels of dissolved oxygen (14 mg l(-1)), egg survival was high and independent of egg size. At low oxygen levels (2.3 mg l(-1)), survival decreased overall, and was higher for large-egged than small-egged siblings. Thus, contrary to conventional expectation, low oxygen levels selected for large rather than small eggs. A second experiment using Atlantic salmon (S. salar) eggs indicated that oxygen consumption increases relatively slowly with increasing egg mass (allometric constant = 0.44). The failure of the conventional 'bigger is worse during incubation' hypothesis may thus be due to the erroneous assumption that oxygen consumption increases at a greater rate with increasing egg mass than does the egg surface area that is available for oxygen diffusion. We also demonstrate, using data from Atlantic salmon, that nest-specific oxygen consumption decreases with increasing egg size, but that this effect is more pronounced for large than for small females. This may help to explain the positive correlation between adult body size and egg size observed in fishes that cluster their eggs.

Animals↗

PubMed2002

Adaptive divergence and the balance between selection and gene flow: lake and stream stickleback in the Misty system.

We investigated the interplay between natural selection and gene flow in the adaptive divergence of threespine stickleback (Gasterosteus aculeatus) that reside parapatrically in lakes and streams. Within the Misty Lake system (Vancouver Island, British Columbia), stickleback from the inlet stream (flowing into the lake) have fewer gill rakers and deeper bodies than stickleback from the lake--differences thought to facilitate foraging (benthic macroinvertebrates in the stream vs. zooplankton in the open water of the lake). Common-garden experiments demonstrated that these differences have a genetic basis. Reciprocal transplant enclosure experiments showed that lake and inlet stickleback grow best in their home environments (although differences were subtle and often not significant). Release-recapture experiments in the inlet showed that lake fish are less well-suited than inlet fish for life in the stream (higher mortality or emigration in lake fish). Morphological divergence in the wild and under common rearing was greater between the lake and the inlet than between the lake and the outlet. Genetic divergence (mitochondrial DNA and microsatellites) was greatest between the lake and the upper inlet (1.8 km upstream from the lake), intermediate between the lake and the lower inlet (0.9 km upstream), and least between the lake and the outlet stream (1.2 km downstream). Relative levels of gene flow estimated from genetic data showed the inverse pattern. The negative association between morphological divergence and gene flow is consistent with the expectation that gene flow can constrain adaptation. Estimated absolute levels of gene flow also implied a constraint on adaptation in the outlet but not the inlet. Our results suggest that natural selection promotes the adaptive divergence of lake and stream stickleback. but that the magnitude of divergence can be constrained by gene flow.

Adaptation, Physiological↗