Unravelling the mystery of the shark genus Mustelus in southern Africa using a multidisciplinary approach

Maduna, Simo Njabulo (2017-12)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Multidisciplinary approaches have previously offered some alternative innovative ways of addressing classical ecological questions while providing novel insights into behaviour and biology of elasmobranch species. The species-rich shark genus Mustelus, or smoothhounds (smoothhound sharks), is one of the most bio-economically important groups of elasmobranchs in the world’s oceans. Despite the commercial value of Mustelus, its systematics remains largely unresolved and the knowledge on the copulating and dispersal strategies of species of Mustelus is scarce. Here, a multidisciplinary approach – molecular, morphology and histology – with different methods of analysis on various spatial scales was used. First, this study investigated the evolutionary origin of the shark genus Mustelus in southern Africa using molecular phylogenetic and statistical biogeography approaches. Results gave strong support for a northern hemisphere origin of southern African Mustelus species, and that the radiation of Mustelus in this region was primarily driven by long-distance dispersal. The monophyly of expanded Mustelus indicated that southern African species of the genus arose from at least two separate colonisation events from the Northern Hemisphere. On a microevolutionary scale, a comparative population genetics approach was used to gain insight into spatial genetic structure and dispersal patterns in species of Mustelus (M. mustelus and M. palumbes) and other co-distributed demersal sharks (Galeorhinus galeus and Triakis megalopterus) characterised by assorted life histories, habitat preferences, and dispersal behaviour. Based on novel Next Generation Sequencing (NGS)-mined microsatellites, the null hypothesis of genetic homogeneity was rejected for all species investigated except for T. megalopterus. Most noteworthy is that the coalescent analysis of migration supported asymmetric gene flow from the Indian to the Atlantic Ocean, concordant with the Atlantic Ocean–Indian Ocean connection via Agulhas leakage proposed for many marine species along the South African coast. In terms of fisheries forensics, a dermal denticle identification key guide and two molecular assays (a microsatellite panel and High-resolution melting assay) were successfully developed for species identification of southern African Mustelus (M. mosis, M. mustelus and M. palumbes) and three other shark species (Galeorhinus galeus, Scylliogaleus quecketti and Triakis megalopterus) commonly confused with species of Mustelus in the region. Additionally, a SNP discovery and genotyping pipeline was optimised that could in future be used to obtain genome-wide data that will enable population genetic and demographic processes of the study species to be assessed more accurately. Lastly, evidence of sperm storage in female common smoothhound sharks was reported for the first time using a histological approach. The molecular analysis of a single common smoothhound litter also hinted at the within-species variation in the presence and frequency of multiple paternity previously reported for elasmobranchs. Overall, this study provides the most comprehensive set of conservation genetic resources for the common smoothhound shark to date. The results provide novel insights into the conservation biogeography, species identification and ecology of dispersal as well as mating behaviours in species of Mustelus. This will help inform existing and ongoing management and conservation efforts for smoothhound sharks occurring in southern Africa.

AFRIKAANSE OPSOMMING: Multi-dissiplinêre benaderings bied alternatiewe innoverende maniere om klassieke ekologiese vrae aan te spreek, terwyl dit nuwe insig in gedrag en biologie van kraakbeenagtige visspesies verskaf. Die spesie-ryk haai genus Mustelus, of gladhonde (gladhondhaaie), is een van die mees bio-ekonomiese belangrike groepe van die kraakbeenagtige visspesies in die wêreld se oseane. Ten spyte van die kommersiële waarde van Mustelus, bly die genus se klassifikasie grootliks onopgelos en die kennis oor die kopulering en verspreidingstrategieë van spesies van Mustelus is skaars. Hier word ‘n multi-dissiplinêre benadering – molekulêre, morfologie en histologie – met verskillende metodes van analiese op verskeie geografiese skale gebruik. Eerstens het hierdie studie die evolusionêre oorsprong van die haai genus Mustelus in suidelike Afrika ondersoek deur gebruik te maak van molekulêre filogenetiese en statistiese biogeografiese benaderings. Resultate het sterk steun verleen vir oorsprong vanaf die noordelike halfrond vir die Suider-Afrikaanse Mustelus spesies, en dat die radiasie van Mustelus in hierdie streek hoofsaaklik deur langafstandverspreiding gedryf is. Die monofilie van uigebreide Mustelus het aangedui dat die Suider-Afrikaanse spesies van die genus ontstaan het uit ten minste twee afsonderlike kolonisasie gebeure uit die noordelike halfrond. Op ‘n mikroevolusionêre skaal, was ‘n vergelykende populasiegenetika-benadering gebruik om insig te verkry in geografiese genetiese struktuur en verspreidingspatrone in Mustelus (M. mustelus and M. palumbes) en ander demersale haai spesies (Galeorhinus galeus and Triakis megalopterus) gekenmerk deur verskillende lewenssiklusse, habitatvoorkeure en verspreidingspatrone. Gebaseer op unieke Volgende Generasie Volgorderbepalings (VGV)-gemynde mikrosatelliete, is die nulhipotese van genetiese homogeniteit verwerp vir alle spesies ondersoek hier behalwe vir T. megalopterus. Mees opmerklik is dat die analise van migrasie assimetriese geenvloei van die Indiese na die Atlantiese Oseaan ondersteun, ooreenstemmend met die Atlantiese Oseaan-Indiese Oseaan verbinding via Agulhas lekkasie voorgestel vir baie mariene spesies langs die Suid-Afrikaanse kus. In terme van vissery forensiese navorsing, was ‘n suksesvolle morfologiese identifikasie gids en twee molekulêre toetse (‘n mikrosatelliet paneel en hoë resolusie smelting toets) ontwikkel vir spesies indentifikasie van Suider-Afrikaanse Mustelus (M. mosis, M. mustelus and M. palumbes) en drie ander haai spesies (Galeorhinus galeus, Scylliogaleus quecketti and Triakis megalopterus) wat algemeen verwar word met Mustelus spesies in die streek. Daarbenewens is ‘n SNP merker ontwikkeling pyplyn geoptimiseer wat in die toekoms gebruik kan word om genoomwye data te verkry wat assessering van populasiegenetiese en demografiese prosesse van die studie spesie sal vergemaklik. Laastens, bewyse van spermberging in vroulike M. mustelus is vir die eerste keer aangemeld met behulp van 'n histologiese benadering. Die molekulêre analise van 'n enkele M. mustelus broeisel het ook aangedui op die binne-spesie variasie in die teenwoordigheid en frekwensie van veelvuldige vaderskap wat voorheen vir kraakbeenagtige visspesies gerapporteer is. In die geheel bied hierdie studie tot op hede die mees omvattende samestelling van bewaringsgenetiese hulpbronne vir die M. mustelus haai. Die resultate bied nuwe insigte in die bewaringsbiogeografie, spesie identifikasie en ekologie van verspreiding asook paring gedrag in Mustelus spesies. Dit sal help om bestaande en deurlopende bestuurs- en bewaringspogings vir hondhaaie wat in Suider-Afrika voorkom in te lig.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102584
This item appears in the following collections: