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

[摘要] 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 toabalone farms distributed in three biogeographic regions up until 2011, when the firstwild 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 anddispersal potential of B. proboscidea. The first objective was to assess the feasibility ofusing a closely related species to ground truth in the predictions. In Chapter 2,reproductive experiments were integrated with molecular studies to show that the nonindigenousoyster pest Polydora hoplura, like B. proboscidea can produce both planktotrophic and adelphophagic larvae (poecilogonous development). Due to a similarreproductive strategy along with its status as an aquaculture pest, P. hoplura waschosen as the 'predictor species. In Chapter 3 I investigated the effect of temperatureon larval development of P. hoplura and B. proboscidea using temperature regimesreflective of the SA coast to determine establishment potential. Results showed thattemperature significantly affected survivorship and developmental rate of planktotrophicand adelphophagic larvae for both species. For P. hoplura, survivorship of both larvaltypes was highest at the intermediate to high temperature treatments (21 and 24°C) andwas generally lower at the lower temperatures (12 and 17°C). Boccardia proboscideaexhibited a difference in survival optima where low temperatures favoured highplanktotroph survival but low adelphophagic larval survival. Conversely, increasedtemperatures favoured high adelphophagic larval survival but low planktotroph survivaland 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 iscongruent with its present distribution. Based on this I predicted that B. proboscideashould become established along a large section of the SA coast and differences insurvival optima may also facilitate its establishment in colder waters where P. hopluraappears to be absent. In Chapter 4, I investigated the phylogeography of P. hoplurausing mtDNA (Cyt b) and nDNA (ATPSα) gene fragments. Results showed geneticconnectivity among all sampling sites distributed across two biogeographic regions. Ihypothesized that the low genetic structure observed was likely due to anthropogenicdispersal mechanisms rather than natural dispersal. Finally in Chapter 5, I discussed thepotential for natural dispersal of B. proboscidea. Based on temperature-specificplanktonic larval duration and current velocities along the SA coast, B. proboscideacould potentially cover hundreds of kilometres in a single generation from each of itsthree point sources. However once the discrepancy between potential and effectivedispersal was accounted for based on the literature, planktotrophic larvae would beexpected to cover considerably shorter distances. When compared to the historicalmovement 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 theworm in its attempt to invade the SA coast but anthropogenic dispersal could be acritical factor facilitating its widespread dispersal.

[发布机构] Stellenbosch University