Opposing genetic patterns of range shifting temperate and tropical gastropods in an area undergoing tropicalisation

Abstract

AimThe poleward range expansion of tropical species, and range contraction of temperate species (known as tropicalisation) has mainly been studied from an ecological perspective, with little research on its genetic consequences. Here, we used distributional and genetic data to document the consequences of tropicalisation in rocky shore gastropods and assess more broadly the future implications of tropicalisation on phylogeographic patterns.LocationNineteen sampling sites along >3000 km of the eastern Pacific rocky intertidal zone, from the tip of the Baja California Peninsula to southern California.TaxonTemperate gastropods: Lottia conus, L. strigatella, Fissurella volcano and Tegula gallina.Tropical gastropods: Fissurella rubropicta, Nerita funiculata and N. scabricosta.MethodsWe determine historical and modern distributions of tropical and temperate species by combining historical records with current field surveys. Using a section of the cytochrome oxidase subunit I gene, we utilised comparative phylogeography, analysis of molecular variance, FST pairwise comparison, mismatch distributions of haplotype differences and neutrality tests to detect genetic signatures of tropicalisation and to better understand its consequences.ResultsWe identified range contractions in two temperate species and range expansion in all three tropical species. We detected genetic signatures of range expansion in the tropical species through unimodal distributions of pairwise haplotype differences and strongly negative values for the Fu and Li D and F* statistics. We found population subdivision and phylogeographic breaks in three temperate species, although the geographic location of the breaks differed among species.Main ConclusionsGenetic signatures and field surveys indicate recent range expansions in tropical species, supporting tropicalisation along the studied coastline. Conversely, we found phylogeographic breaks in temperate species, suggesting that tropicalisation may cause genetic erosion of evolutionary distinct lineages with range‐contraction. The different locations of the phylogeographic breaks among temperate species suggests that some barriers are species specific.

Pushed waves, trailing edges, and extreme events: Eco‐evolutionary dynamics of a geographic range shift in the owl limpet, Lottia gigantea

“…We found genomic structuring mainly within trailing‐edge populations. Consistent with other phylogeographic studies within the region (Bernardi et al., 2003; Eberl et al., 2013; Fenberg et al., 2014; Mares‐Mayagoitia et al., 2023; Zarzyczny et al., 2024), our genomic dataset shows two major clusters, with a dominant break near Punta Eugenia, Mexico. Both topography and ocean currents can impede gene flow between marine metapopulations across this break.…”

“…We found genomic structuring mainly within trailingedge populations. Consistent with other phylogeographic studies within the region (Bernardi et al, 2003;Eberl et al, 2013;Fenberg et al, 2014;Mares-Mayagoitia et al, 2023;Zarzyczny et al, 2024) Zaytsev et al, 2003). We also found a phylogeographic break within the Los Angeles region (LAR, ca.…”

“…Several studies suggest that past climatic‐driven range dynamics are stronger predictors of genetic diversity than contemporary demographic patterns, and can lead to marginal populations being highly diverse (Chefaoui & Serrão, 2017; Hewitt, 2004; Petit, 2003; Zarzyczny et al., 2024). We found that the southern edge of the range had higher climatic suitability at the LGM, which suggests that this region could have high genetic diversity due to it being a climatically stable refugium (Beatty & Provan, 2011; Hellberg et al., 2001; Waltari & Hickerson, 2013; Zarzyczny et al., 2024). The Moments demographic analyses suggest that Baja_cluster and South_cluster have a shared demographic history and thus were similarly impacted by the changes since the LGM.…”