An integrated larval development and population genetics approach for predicting the establishment and dispersal potential of a recently introduced polychaete (Annelida: Spionidae) in southern Africa

David, Andrew Anthony (2015-03)

Thesis (PhD) -- Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Boccardia proboscidea is a recently introduced polychaete in South Africa (SA) where it is a notorious pest of commercially reared abalone. The species was restricted to abalone farms distributed in three biogeographic regions up until 2011, when the first wild population was detected in the southern part of the country. If Boccardia proboscidea becomes invasive, it could pose a threat to the intertidal marine ecosystem of SA. The overarching aim of this thesis was therefore to predict the establishment and dispersal potential of B. proboscidea. The first objective was to assess the feasibility of using a closely related species to ground truth in the predictions. In Chapter 2, reproductive experiments were integrated with molecular studies to show that the nonindigenous oyster pest Polydora hoplura, like B. proboscidea can produce both planktotrophic and adelphophagic larvae (poecilogonous development). Due to a similar reproductive strategy along with its status as an aquaculture pest, P. hoplura was chosen as the “predictor” species. In Chapter 3 I investigated the effect of temperature on larval development of P. hoplura and B. proboscidea using temperature regimes reflective of the SA coast to determine establishment potential. Results showed that temperature significantly affected survivorship and developmental rate of planktotrophic and adelphophagic larvae for both species. For P. hoplura, survivorship of both larval types was highest at the intermediate to high temperature treatments (21 and 24°C) and was generally lower at the lower temperatures (12 and 17°C). Boccardia proboscidea exhibited a difference in survival optima where low temperatures favoured high planktotroph survival but low adelphophagic larval survival. Conversely, increased temperatures favoured high adelphophagic larval survival but low planktotroph survival and this was most likely driven by increased rates of sibling cannibalism. There was also a positive relationship between temperature and developmental rate for both larval types of both species. Polydora hoplura’s response to experimental temperatures is congruent with its present distribution. Based on this I predicted that B. proboscidea should become established along a large section of the SA coast and differences in survival optima may also facilitate its establishment in colder waters where P. hoplura appears to be absent. In Chapter 4, I investigated the phylogeography of P. hoplura using mtDNA (Cyt b) and nDNA (ATPSα) gene fragments. Results showed genetic connectivity among all sampling sites distributed across two biogeographic regions. I hypothesized that the low genetic structure observed was likely due to anthropogenic dispersal mechanisms rather than natural dispersal. Finally in Chapter 5, I discussed the potential for natural dispersal of B. proboscidea. Based on temperature-specific planktonic larval duration and current velocities along the SA coast, B. proboscidea could potentially cover hundreds of kilometres in a single generation from each of its three point sources. However once the discrepancy between potential and effective dispersal was accounted for based on the literature, planktotrophic larvae would be expected to cover considerably shorter distances. When compared to the historical movement of other introduced marine invertebrates in the region, these adjusted distances appear to better reflect the reality of larval dispersal along the SA coast. Boccardia proboscidea benefits from a versatile reproductive strategy which may aid the worm in its attempt to invade the SA coast but anthropogenic dispersal could be a critical factor facilitating its widespread dispersal.

AFRIKAANSE OPSOMMING: Boccardia proboscidea het onlangs in Suid-Afrika (SA) begin voorkom, waar die polychaete ‘n bekende plaag in kommersiële perlemoen is. Die spesie was aanvanklik beperk tot perlemoen plase van drie biogeografiese streke, maar in 2011 is die eerste wilde populasie aan die suidelike kus van die land gevind. Indien B. proboscidea ‘n indringer word, kan dit ‘n bedreiging inhou vir die mariene ekosisteme van Suid-Afrika. Die algehele doel van hierdie tesis was dus om die potensiele verspreiding en vestigings vermoë van B. proboscidea in Suid-Afrika te voorpel. Die eerste objektief was om die moontlikheid te ondersoek om ‘n naverwante kandidaat spesie te gebruik wat die voorspellings rondom B. proboscidea in die werkliheid te kan toets. In Hoofstuk 2, is voorplantings eksperimente met molekulêre studies geintigreer om te wys dat die uitheemse oester plaag, Polydora hoplura, net soos B. proboscidea, beide planktotrofiese en adelfofagiese larwes (poekilogeen ontwikkeling) kan produseer. Danksy die feit dat P. hoplura ‘n soortgelykie voortplantings strategie en status as akwatiese pes het, is dit as ‘n “voorspeller” spesie gekies. In Hoofstuk 3 ondersoek ek die effek van temperatuur op larvi ontwikkeling van B. proboscidea en P. hoplura deur temperatuur toestande te gebruik wat verteenwoordigend van die Suid-Afrikaanse kus is, om hierdeur die vestigings potensiaal te bepaal. Die resultate het getoon dat temperatuur oorlewing en die groei tempo van planktotrofiese en adelphofagiese larwes van albei spesies aansienlik affekteer. Vir P. hoplura was die oorlewing van albei larvi tipes die hoogste vir intermediêre tot hoë temperatuur behandelinge (21 en 24°C) en meestal laer teen laer temperature (12 en 17°C). B. proboscidea het verskillende oorlewings optima getoon, waar laer temperature hoër planktotrofiese oorlewing bevorder maar laer adelphofagiese larwes oorlewing veroorsaak. Inteendeel, verhoogte temperature het hoër adelphofagiese larwes oorlewing bevorder maar laer planktotrofiese oorlewing: dit was moontlik as gevolg van verhoogte tempo’s van kannibalisme. P. hoplura se reaksie op eksperimentiële temperature is in ooreenstemming met die spesie se huidige verspreiding. Gebasseer op die bogenoemde het ek voorspel dat B. proboscidea gevestig sal raak langs groot dele van die Suid-Afrikaanse kus en dat verskille in oorlewings optima die vestiging in kouer waters kan aanhelp waar P. hoplura bleik om afwesig te wees. In Hoofstuk 4, ondersoek ek die pylogeografie van P. hoplura deur gebruik te maak van mtDNA (Cyt b) en nDNA (ATPSα) geen fragmente. Resultate toon ‘n gekonekteerde genetika tussen al die studie areas van twee biogeografiese streke. Ek stel die hipotese dat die lae genetiese struktuur moontlik deur antropogeniese verspreidings meganismes eerder as deur natuurlike verspreiding veroorsaak word. Laastens, in Hoofstuk 5, het ek die potensiaal vir natuurlike verspreiding van B. proboscidea bespreek. Gebasseer op die temperatuur-spesifieke planktoniese larvi duur en stroom snelhede langs die Suid-Afrikaanse kus, kan B. proboscidea moontlik honderde kilometres dek in ‘n enkelle generasie vanaf slegs drie puntbronne van die spesie. Waaneer die verskil tussen potensiële en effektiewe verspreiding in ag geneem word, volgens die literatuur, kan daar van planktoniese larvi verwag word om aansienlike korter afstande te beweeg. Indien geskiedkundige bewegings van uitheemse mariene invertebraat spesies in die area ondersoek word, blyk dit dat die aangepaste afstande ‘n beter voorstelling van werklike larvi verspreiding langs die Suid-Afrikaanse kus skep. Boccardia proboscidea het die voordeel van ‘n aanpasbare voortplantings strategie wat die wurm moontlik kan aanhelp om ‘n indringer aan die Suid-Afrikaanse kus te word. Antropogeniese verspreiding kan ook wel ‘n belangrike faktor wees wat ‘n wye verspreiding aanspoor.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96594
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