Variations in phenotypic plasticity in a cosmopolitan copepod species across latitudinal hydrographic gradients

Abstract

Studies assessing latitudinal variations in habitat conditions and phenotypic plasticity among populations yield evidence of the mechanisms governing differentiation in the potential to adapt to current/future habitat changes. The cosmopolitan copepod species Acartia tonsa thrives across ocean clines delimiting Seasonal (30–40° S) and Permanent (10–30° S) Upwelling coastal provinces established during the middle–late Pliocene (3.6–1.8 Ma) alongshore the South East Pacific (SEP), nowadays exhibiting contrasting variability features related to several ocean drivers (temperature, salinity, pH, and food availability). Latitudinal variation across the range of environmental conditions of the coastal provinces can contribute toward shaping divergent A. tonsa’s phenotypes, for example, through specific patterns of phenotypic plasticity in morphological and physiological traits and tolerance to environmental drivers. With the aim of contributing to the understanding of these adaptive processes in a relatively little studied oceanic region, here we compared the expression of parental (i.e., adult size, egg production, and ingestion rate) and offspring (i.e., egg size) traits in relation to variation in environmental habitat conditions across different cohorts of two distant (> 15° latitude) A. tonsa populations inhabiting estuarine and upwelling habitats located in the Seasonal and Permanent Upwelling province, respectively. Mean conditions and ranges of variability in the habitat conditions and phenotypic plasticity of parental and offspring traits within and among cohorts of A. tonsa populations varied significantly across the different examined regions (i.e., Seasonal vs. Permanent). We also found significant differences in the coupling of habitat variability and trait expression, suggesting that the differences in trait expressions might be related to habitat variability. The phenotypic divergence was translated to cohort-related patterns of trait trade-offs regulating reproduction and tolerance of egg production efficiency that can jointly determine the level of plasticity, genetic structure, or local adaptation. The current findings provide novel evidence of how divergent phenotypes might sustain A. tonsa populations across variable coastal provinces of the SEP.

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

“…These traits include a broad tolerance to environmental fluctuations and the production of large cohorts 27 , 77 , 78 . Ecology and physiology studies have shown that populations previously identified as A. tonsa off the coast of Chile, including populations studied here, used mechanisms of tolerance and plasticity to face extreme environmental conditions 34 , 49 , and populations of different biogeographical areas showed signs of adaptation to local conditions of their habitat 34 . When we analyzed the genetic variation of both mitochondrial and nuclear markers between populations and biogeographic areas, we observed high genetic variability within populations, which was consistent with the levels of genetic diversity (Table 1 ).…”

“…The populations of this new species are more closely related phylogenetically to other endemic species of genus Acartia to the Pacific Ocean than to Acartia tonsa . Additionally, our results suggest that although connectivity between the populations studied here is possible mainly due to the action of Humboldt current system, the geographical distances and contrasting environmental conditions 34 , 52 may be the main structures of the genetic diversity of the copepod populations that inhabit the SEPO region.…”

“…Significant values are in bold. www.nature.com/scientificreports/ For decades, the presence of A. tonsa has been documented along the coast of Chile, with numerous ecological studies conducted on these populations 34,[46][47][48][49]76 . In these studies, it was expected that A. tonsa populations from the Chilean coast would exhibit a range of physiological and life history traits characteristic of cosmopolitan species, such as A. tonsa found in other oceans and seas worldwide.…”

“…The Acartia ability to tolerate a broad range of salinity (0.3-36.9 psu) and temperature (− 1 to 32 °C) 29,30 enables this species to achieve a wide distribution. Consequently, its ecology and evolution has been extensively studied [31][32][33][34] . At the central and southern coast of SEPO, the population density of A. tonsa depends mainly on food availability (mainly microplankton), exhibiting a marked seasonality in abundance on the central and southernmost coast of SEPO 35,36 .…”

“…To date, the presence of A. tonsa in SEPO coastal systems has been identified solely based on morphological characteristics, without molecular confirmation. In this context, it is crucial to emphasize that despite multiple studies on the distribution, physiology, and life history of populations along the coasts of Chile, there are no molecular sequences of A. tonsa available for the SEPO 34,[46][47][48][49] . The SEPO, specifically the coastal domain along the Chilean coast (18-56° S), provides a unique natural setting for studying the population dynamics of planktonic coastal species.…”