Integrated genetic and morphological data support eco‐evolutionary divergence of Angolan and South African populations of Diplodus hottentotus

Abstract

The genus Diplodus presents multiple cases of taxonomic conjecture. Among these the D. cervinus complex was previously described as comprising three subspecies that are now regarded as separate species: Diplodus cervinus, Diplodus hottentotus and Diplodus omanensis. Diplodus hottentotus exhibits a clear break in its distribution around the Benguela Current system, prompting speculation that Angolan and South African populations flanking this area may be isolated and warrant formal taxonomic distinction. This study reports the first integrated genetic [mitochondrial (mt)DNA and nuclear microsatellite] and morphological (morphometric, meristic and colouration) study to assess patterns of divergence between populations in the two regions. High levels of cytonuclear divergence between the populations support a prolonged period of genetic isolation, with the sharing of only one mtDNA haplotype (12 haplotypes were fully sorted between regions) attributed to retention of ancestral polymorphism. Fish from the two regions were significantly differentiated at a number of morphometric (69·5%) and meristic (46%) characters. In addition, Angolan and South African fish exhibited reciprocally diagnostic colouration patterns that were more similar to Mediterranean and Indian Ocean congeners, respectively. Based on the congruent genetic and phenotypic diversity we suggest that the use of hottentotus, whether for full species or subspecies status, should be restricted to South African D. cervinus to reflect their status as a distinct species-like unit, while the relationship between Angolan and Atlantic-Mediterranean D. cervinus will require further demo-genetic analysis. This study highlights the utility of integrated genetic and morphological approaches to assess taxonomic diversity within the biogeographically dynamic Benguela Current region.

Genetic analysis provides insights into species distribution and population structure in East Atlantic horse mackerel (Trachurus trachurus and T. capensis)

“…There was no significant mtDNA differentiation between the T. capensis samples from Angola and South Africa. This is a striking result in light of the high level of mtDNA divergence, including examples of reciprocal monophyly, between Angolan and South African sites for a number of marine taxa due to the BUS biogeographic boundary (Gwilliam et al ., ; Henriques et al ., , ; Reid et al ., ). This could be due to a combination of the previously mentioned slow mtDNA mutation rates for Trachurus as well as effective gene flow across the BUS as might be expected based on the species' life history.…”

Deep phylogeographic structure may indicate cryptic species within the Sparid genus Spondyliosoma

“…The BUS has been identified as the prominent driver of divergence across the SE Atlantic region, generating isolated populations as well as endemic lineages and species in South African waters (Gwilliam et al, 2018; Henriques et al, 2012, 2014; Reid et al ., 2016; Sala‐Bozano et al ., 2009; Schwaninger, 2008; Teske et al ., 2011). However, for some groups the BUS exhibits varying levels of historical and/or recurrent permeability permitting bi‐directional (Henriques et al ., 2015) or asymmetric (Healey et al ., 2017) gene flow.…”

“…In addition, ratios of within/between clade sequence divergence exceed barcode gaps for species delineation suggested for fish (Ward et al ., 2009). In light of criticisms of species delimitation based solely on mtDNA (reviewed in Hudson & Coyne, 2002; Hudson & Turelli, 2003; Moritz & Cicero, 2004; Sites & Marshall, 2004) confirmatory evidence from other approaches is recommended (Funk & Omland, 2003; Gwilliam et al ., 2018). Nuclear F ST were also significant in all comparisons between the S. emarginatum and Angola samples (with no differentiation within ether group), confirming restricted biparental gene flow between the groups.…”

“…The BUS has been identified as the prominent driver of divergence across the SE Atlantic region, generating isolated populations as well as endemic lineages and species in South African waters (Gwilliam et al, 2018;Henriques et al, 2012Henriques et al, , 2014Reid et al, 2016;Sala-Bozano et al, 2009;Schwaninger, 2008;Teske et al, 2011).…”

“…However, for some groups the BUS exhibits varying levels of historical and/or recurrent permeability permitting bi-directional (Henriques et al, 2015) or asymmetric (Healey et al, 2017) T A B L E 4 Summary of nuclear genetic variation for the Mossel Bay, False Bay, Namibe and Benguela samples described using allele number (N a ), allelic richness (A R ), expected (H E ) and observed (H O ) heterozygosities and probability of conformance to the Hardy-Weinberg equilibrium (P HWE ) of within/between clade sequence divergence exceed barcode gaps for species delineation suggested for fish (Ward et al, 2009). In light of criticisms of species delimitation based solely on mtDNA (reviewed in Hudson & Coyne, 2002;Hudson & Turelli, 2003;Moritz & Cicero, 2004;Sites & Marshall, 2004) confirmatory evidence from other approaches is recommended (Funk & Omland, 2003;Gwilliam et al, 2018). Nuclear F ST were also significant in all comparisons between the S. emarginatum and Angola samples (with no differentiation within ether group), confirming restricted biparental gene flow between the groups.…”