Conectividade genética, filogeografia e conservação de tubarões pelágicos no Oceano Atlântico ocidental
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Data
2016-12-12
Autores
Domingues, Rodrigo Rodrigues [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As espécies Carcharhinus falciformis e Carcharhinus signatus, são tubarões oceânicopelágicos, caracterizados por habitarem o ambiente epipelágico de águas quentes e temperados de todo o mundo. Devido ao alto valor da suas nadadeiras, estas espécies são demasiadamente capturadas pela pesca de espinhel pelágico, direcionado para a captura de atuns e espadarte. Em decorrência dessa severa pressão pesqueira, estima-se que estas espécies tiveram reduções populacionais em torno de 75%, e estão atualmente listadas como próximo de ameaçada (C. falciformis) e vulnerável (C. signatus) na lista vermelha da Internation union for Conservation of Nature (IUCN). Por serem espécies migratórias e por habitarem águas internacionais, as ações de conservação exigem esforços conjuntos de vários países, tarefa que no Oceano Atlântico compete à International Commission for the Conservation of Atlantic Tunas – ICCAT. A presente tese avaliou os aspectos genéticos populacionais e filogeográficos de ambas espécies, utilizando marcadores moleculares mitocondriais (C. falciformis e C. signatus) e microssatélites (C. signatus). Especificamente, foram avaliados os níveis de diversidade genética, testada a hipótese nula de panmixia e inferidos os cenários filogeográficos responsáveis pelas relações filogenéticas intraespecíficas, e aspectos demográficos populacionais. Além disso, a diversidade genética da subclasse elasmobrânquios foi avaliada e discutida a sua utilização nas avaliações do estado de conservação de espécies e políticas afins. A diversidade genética total para ambas as espécies, utilizando a região controle do DNA mitocondrial foi alta (h = 0,88±0,012 e π = 0,005±0,003 – C. falciformis; h = 0,74±0,027 e π = 0,0034±0,0019 – C. signatus), No entanto, C. signatus apresentou baixos valores para o Atlântico Sul Ocidental (h = 0,545±0,077 e π = 0,0013±0,0009) e para 9 loci microssatélites (Ho = 0,40). A hipótese nula de panmixia foi rejeitada para C. falciformis (ΦST 0.058, P < 0.0001) e C. signatus, ambas espécies apresentando estrutura genética populacional entre localidades do Hemisfério norte e Hemisfério sul. Carcharhinus signatus apresentou uma dispersão baseada em sexo, com machos panmíticos e fêmeas estruturadas (ΦST = 0,443; P < 0,01), um típico padrão de filopatria reprodutiva, corroborado pelo isolamento-por-distância (r = 0,65, p = 0,03). Duas linhagens matrilineais foram verificadas para ambas espécies, formadas há 485, 571 Kya (C. falciformis) e 166, 598 Kya (C. signatus), correspondendo ao Pleistoceno. A hipótese de expansão populacional não pode ser rejeitada para ambas espécies, iniciando durante o último máximo glacial – UMG para C. falciformis, enquanto que C. signatus passou por um efeito gargalo no UMG, seguido de uma expansão populacional no Holoceno. Uma exaustiva revisão bibliográfica, revelou um aumento considerável nos últimos anos dos estudos genéticos populacionais que descrevem a diversidade genética de tubarões e raias. Além disso, as métricas de diversidade genética revelaram que, em geral, os elasmobrânquios possuem baixa variabilidade genética, sobretudo para os marcadores mitocondriais. Por fim, foi discutida a inclusão dessas métricas nas avaliações do estado de conservação de espécies e políticas afins.
The shark species, Carcharhinus falciformis and Carcharhinus signatus, are oceanic-pelagic species that inhabit tropical, subtropical and temperate waters worldwide. The high value of their fins associated with the by-catch these species by longline fisheries, which targeting tuna and swordfish, has led to a population reduction around 75%. Currently, these species are listed on the IUCN Red list as Near Threatened (C. falciformis) and Vulnerable (C. signatus). Due to their high vagility and migratory behavior, inhabiting internation waters, management and conservation plans require joint efforts from the many country, a task that in the Atlantic Ocean is entrusted to the International Commission for the Conservation of Atlantic Tunas – ICCAT. This Thesis assessed the main aspects of population genetics and phylogeography in both species. Using mitochondrial marker (C. falciformis and C. signatus) and nine loci microsatellites (C. signatus). Especifically, the levels of genetic diversity were assessed, panmixia null hypothesis was tested and the phylogeography scenarios responsible for intraspecific phylogenetic relationships and populations demography were inferred. Furthermore, the genetic diversity of subclass Elamosbranchii and its usefullness to assess conservation policies were discussed. The overall genetic diversity at CR mtDNA in both species was high (h = 0.88±0.012 and π = 0.005±0.003 – C. falciformis; h = 0.74±0.027 and π = 0.0034±0.0019 – C. signatus). However, C. signatus showed low genetic diversity values in the Southwestern Atlantic (h = 0.545±0.077 and π = 0.0013±0.0009) and at 9 loci microsatellites (Ho = 0.40). The null hypothesis of panmixia was rejected for C. falciformis (ΦST 0.058, P < 0.0001) and C. signatus, with both species showing population structured along the western Atlantic Ocean. Carcharhinus signatus showed sex-based dispersion, with male roving and female no roving (ΦST = 0.443; P < 0.01), indicating reproductive phylopatry, supported by isolation-by-distance (r = 0.65, P = 0,03). The Maximum likelihood and Bayesian tree presented two matrilineal lineages to both species, with split started 485, 571 Kya (C. falciformis) and 166, 598 Kya (C. signatus), corresponding to Pleistocene. The hypothesis of population expansion cannot be rejected to both species, starting during the last glacial maximum – LGM for C. falciformis, whereas C. signatus passed through a bottleneck effect, followed of population expansion in the Holecene. An exhaustive bibliography revision revelead a considerable increase of genetic population studies of sharks and rays. Moreover, metanalysis of genetic diversity metrics revealed that shark and rays, in general, have low genetic diversity, mainly for mitochondrial markers. Finally, the inclusion of genetic diversity metrics in species assessent and conservation policies was discussed.
The shark species, Carcharhinus falciformis and Carcharhinus signatus, are oceanic-pelagic species that inhabit tropical, subtropical and temperate waters worldwide. The high value of their fins associated with the by-catch these species by longline fisheries, which targeting tuna and swordfish, has led to a population reduction around 75%. Currently, these species are listed on the IUCN Red list as Near Threatened (C. falciformis) and Vulnerable (C. signatus). Due to their high vagility and migratory behavior, inhabiting internation waters, management and conservation plans require joint efforts from the many country, a task that in the Atlantic Ocean is entrusted to the International Commission for the Conservation of Atlantic Tunas – ICCAT. This Thesis assessed the main aspects of population genetics and phylogeography in both species. Using mitochondrial marker (C. falciformis and C. signatus) and nine loci microsatellites (C. signatus). Especifically, the levels of genetic diversity were assessed, panmixia null hypothesis was tested and the phylogeography scenarios responsible for intraspecific phylogenetic relationships and populations demography were inferred. Furthermore, the genetic diversity of subclass Elamosbranchii and its usefullness to assess conservation policies were discussed. The overall genetic diversity at CR mtDNA in both species was high (h = 0.88±0.012 and π = 0.005±0.003 – C. falciformis; h = 0.74±0.027 and π = 0.0034±0.0019 – C. signatus). However, C. signatus showed low genetic diversity values in the Southwestern Atlantic (h = 0.545±0.077 and π = 0.0013±0.0009) and at 9 loci microsatellites (Ho = 0.40). The null hypothesis of panmixia was rejected for C. falciformis (ΦST 0.058, P < 0.0001) and C. signatus, with both species showing population structured along the western Atlantic Ocean. Carcharhinus signatus showed sex-based dispersion, with male roving and female no roving (ΦST = 0.443; P < 0.01), indicating reproductive phylopatry, supported by isolation-by-distance (r = 0.65, P = 0,03). The Maximum likelihood and Bayesian tree presented two matrilineal lineages to both species, with split started 485, 571 Kya (C. falciformis) and 166, 598 Kya (C. signatus), corresponding to Pleistocene. The hypothesis of population expansion cannot be rejected to both species, starting during the last glacial maximum – LGM for C. falciformis, whereas C. signatus passed through a bottleneck effect, followed of population expansion in the Holecene. An exhaustive bibliography revision revelead a considerable increase of genetic population studies of sharks and rays. Moreover, metanalysis of genetic diversity metrics revealed that shark and rays, in general, have low genetic diversity, mainly for mitochondrial markers. Finally, the inclusion of genetic diversity metrics in species assessent and conservation policies was discussed.
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Palavras-chave
Estrutura genética populacional, Diversidade genética, Marcador molecular, Elasmobrânquios