Explorando os efeitos do ambiente sobre a diversidade genética e a conectividade de populações da sardinha-cascuda brasileira Harengula sp

Abstract

Biodiversity loss is currently a major concern in conservation and evolutionary biology. Global warming can aggravate this scenario, as numerous species are already living closer to their thermal limits, especially tropical ones. Understanding the environmental features that drive population dynamics is an important step towards establishing the sustainable use of natural resources, once the environment influence species’ distribution, diversity and, ultimately, their evolution. In the present thesis, divided in three chapters, I used genomic and ecological data to understand how the environment guides the evolution of scaled sardines Harengula sp., a putative undescribed species at the Brazilian coast. In the first chapter, I estimated how past climatic cycles impacted the demographic history of Harengula sp. in the Atlantic Southwest. I found that this lineage is structured by depth and salinity in two populations that reflect the shallow-water habitat expansion following the LGM: a large, more diverse and expanding at the Brazilian coast, (coastal population, Ne 3.6) and a smaller, which contracted to a third the size of an ancestral population at the oceanic archipelago of Fernando de Noronha (FNO, island population, Ne 0.3). The status of the FNO population is more sensible, considering that Harengula sp. is of fundamental commercial and ecologic importance as the only sardine species in the archipelago, where conflicts remain unsolved between park managers and local fishers demanding the exploitation of this fishery in the park’s no-take zone. High differentiation (Fst 0.17) despite symmetric gene flow between coastal and insular populations reinforces the need for different management strategies for these two populations. In the second chapter, I investigated the dynamics of habitat occupation in the present climate and estimated habitat change given a future of global warming. Niche modelling indicates southward shift and range contraction of environmental suitability for the scaled sardines Harengula sp., a change that increases as the scenarios modelled for the future are aggravated. Larval dispersal models indicate that marine protected areas (MPAs) in islands, such as FNO, Abrolhos, and Rocas Atoll, currently act as a biodiversity and fishery spillover to the coastal mainland, potentially minimizing the effects of overfishing at the Brazilian coast and increasing population resilience to cope with habitat change. However, distantly located MPAs (>1,000 km) such as Trindade-Martim Vaz, are not a source of sardines’ larvae to the coast. The larval connection between FNO and the Brazilian coast reflects the genetic admixture between coastal and island populations aforementioned, demonstrating the dispersal potential of early life stages of this species. In the third chapter, I tested the effects of the environment on the structure of coastal and island (FNO) populations, testing the hypothesis of climatic stability over time harbour higher genetic diversity. I found no statistically significant correlation between the environmental features (present suitability and climatic stability) and genetic patterns tested (nucleotide diversity and demography). Here, the model that considers only geographic distance is the best to explain the patterns of genomic diversity of Harengula sp., reflecting the pattern of isolation by distance indicated in chapter 1. In this thesis, combining methods allowed uncovering genetic diversity, detecting population dynamics, estimating dispersal ability, habitat change and its impacts on the evolutionary trajectory of an undescribed marine species in the Atlantic Southwest.