Local scale extreme low pH conditions and genetic differences shape phenotypic variation in a broad dispersal copepod species

Abstract

Extreme low pH events in estuaries and upwelling areas can modulate the phenotypic and genetic diversity of natural populations. To test this hypothesis, we explored the linkage between local scale extreme low pH events, genetic diversity, and variation in fecundity-related traits (body size, egg size, and egg production rate) in the broad-dispersal copepod Acartia tonsa. We assessed genetic and phenotypic characteristics of populations by contrasting extreme low pH environments (upwelling and temperate estuary) in the coastal Southeast Pacific, under natural and experimental conditions. These populations showed significant genetic differentiation with higher diversity in mitochondrial and nuclear loci (encoding mtCOI and 18S rRNA) in the estuarine population. Copepods from this population are exposed to more frequent extreme low pH events (< 7.7), and the adult females exhibit consistent phenotypic variation in body size, egg size, and egg production rate across different cohorts. Experimental acclimation to extreme low pH conditions revealed no significant differences in fecundity-related traits between A. tonsa populations. Although these results partially support our hypothesis, the experimental findings suggest other drivers might also influence phenotypic differences in the local environments.

Molecular evidence for a new endemic species of Acartia (Copepoda, Calanoida) from the Southeast Pacific coast

“…Our research group and other authors have repeatedly characterized the variability of the coastal ocean environment in the localities under study 52 , 82 – 84 , accounting for considerable differences between localities in temperature, salinity, PCO 2 , food availability related to the different biogeographical zones. Broadly speaking, higher temperatures prevail in the Peruvian province, which decrease with increasing latitude 84 .…”

“…Broadly speaking, higher temperatures prevail in the Peruvian province, which decrease with increasing latitude 84 . Regarding salinity, this is higher in the Peruvian province and decreases in the other provinces, being directly dependent on the contribution of fresh water from the rivers, which increases in winter 82 , 84 . In the Peruvian province and in the intermediate area, episodic events of high ocean acidification (PCO 2 ~ 1800 μatm) can be found, mainly associated with upwelling areas and river discharges 52 , 83 .…”

“…In the Peruvian province and in the intermediate area, episodic events of high ocean acidification (PCO 2 ~ 1800 μatm) can be found, mainly associated with upwelling areas and river discharges 52 , 83 . Finally, it has been observed that the concentration of food is higher and less variable in estuarine localities of the intermediate area than in upwelling areas of the Peruvian province 84 . Detailed information on the main environmental conditions of each population studied in Suppl.…”

“…Our research group and other authors have repeatedly characterized the variability of the coastal ocean environment in the localities under study 52,[82][83][84] , accounting for considerable differences between localities in temperature, salinity, PCO 2 , food availability related to the different biogeographical zones. Broadly speaking, higher temperatures prevail in the Peruvian province, which decrease with increasing latitude 84 . Regarding salinity, this is higher in the Peruvian province and decreases in the other provinces, being directly dependent on the contribution of fresh water from the rivers, which increases in winter 82,84 .…”