Molecular and Fitness Data Reveal Local Adaptation of Southern and Northern Estuarine Oysters (Crassostrea ariakensis)

Abstract

Natural selection and isolation are both important for understanding the geographic distribution of marine species and environmental responses to changing climate. In this study, we revealed distinct genetic variation in Crassostrea ariakensis by comparing the COI gene segment sequence in northern and southern oysters partitioned by the Yangtze River estuary. Reciprocal hybridization and intrapopulation crosses clarified their taxonomic status as the same species. There was no heterosis in the survival and growth of the hybrids, while the maternal effect was observed in larvae from eggs in the native habitat that showed higher fitness. Both the northern and southern F 1 progenies exhibited positive performance in fitness traits, including survivorship, respiration rate, and growth, in their native habitats compared to that in their non-native habitats, indicating a strong signature of local adaptation. The oysters dwelling in the warm/southern habitats evolved a higher thermotolerance of LT 50 , while the oysters inhabiting the high-salinity/northern habitats had a 2.43 higher LS 50 than that of their southern counterparts. After strong natural selection in the northern environments, the higher survival of the F 1 progenies from the southern oysters under heat shock indicates an evolved genetic basis for its higher thermal tolerance. Strong environmental gradients, especially for temperature and salinity, and geographic isolation by the interaction between coastal currents and the Yangtze River estuary potentially contribute to shaping the distribution pattern and adaptive divergence of C. ariakensis in China.

Genome of the estuarine oyster provides insights into climate impact and adaptive plasticity

“…S7). Salinity at the northern BZ site was 10.98 ‰ higher than the southern TS site ( 3 ). Climate change may enhance the difference and cause salinity to increase at north habitats but decrease at south habitats ( 45, 46 ).…”

“…Thus, temperature and salinity are the two most important environmental factors driving adaptive divergence between northern and southern populations. With discontinuous distribution and limited gene flow, the southern population became locally adapted and evolved higher tolerance to high temperature and low salinity ( 3 ). We expect that some genomic regions were subjected to selection and contributed to adaptation to higher temperature and lower salinity conditions in the southern population.…”

“…To explore the plasticity of candidate genes from regions under selection, we measured transcriptional changes in oysters subjected to native and non-native environments after reciprocal transplantation ( 3 ). Briefly, wild oysters derived from northern (Binzhou: BZ, Bohai Sea) and southern (Taishan: TS, East China Sea) environments were collected and used to produce F 1 progeny.…”

“…Sea levels are rising, and ocean circulation patterns are changing. With the rising of global temperature, dry regions are getting drier, while wet regions become wetter ( 2 ), increasing salinity difference among estuaries ( 3 ). These rapid changes in world’s oceans are having a significant impact on marine ecosystems, much of which remains poorly understood.…”

Northward shift of a biogeographical barrier on China’s coast

“…Along China's coast, the YRE has been regarded as a coastal biogeographical boundary separating two ecological provinces for marine species, the Cold Temperate Northwest Pacific Province and the Warm Temperate Northwest Pacific Province (Dong et al, 2012;Liu, 2013;Ni et al, 2017;Xu et al, 2020;Yan et al, 2019). Previous studies that examined marine bivalves (Li et al, 2020;Ni et al, 2014Ni et al, , 2015, gastropods (Dong et al, 2012;Qu et al, 2021;Wang et al, 2016;Zhao et al, 2017), crustaceans (Cheng et al, 2020;Han et al, 2015), polyplacophorans (Ni et al, 2020) and macroalgae (Cheang et al, 2010;Ni et al, 2020) have indicated the barrier impacts of the YREBB on species biogeographic and phylogeographic patterns. The formation of the YERBB is closely related to habitat continuity, historical events, oceanographic features and climate factors (Figure 2).…”