Abstract
The asterinid seastars Parvulastraparvivipara and P.vivipara share atypical viviparous reproductive modes that have made them of interest for research on life-history evolution and population genetics. This article briefly reviews life-history traits of these endemic Australian species and information on distribution and rarity, as well as providing some additional new analysis. Almost exclusive self-fertilisation has led to extreme genetic poverty in both species and viviparity limits dispersal potential causing relatively small geographical ranges. There is some evidence that the number of intertidal boulder-fields harbouring P.parvivipara, and the overall geographical range, may have become reduced in recent years. In addition, approximately 25 % of boulder-fields with P.parvivipara have been colonised by invasive oysters (Magallanagigas). To understand potential effects of oysters on P.parvivipara, we tested for correlations between P.parvivipara abundances and cover of oyster encrustations that included this invader (native + non-native oyster shells were assessed together because they produced similar encrustations and largely could not be differentiated). Linear regression showed no evidence, however, for any correlation. For P.vivipara, population survey data from the mid 1970’s to present shows marked decline in areas of previous abundance. Parallel with this decline, the boulder habitat has experienced infill and siltation and cementing of the substratum by M.gigas, sponges and other encrusters as well as anoxia. Important future research outcomes on consequences of atypical life-history traits may be allowed by continued research on these seastars but only if their populations are able to persist within the small number of boulder-fields where they occur. Current trends may indicate a need for conservation intervention.
Highlights
Life-history traitsParvulastra parvivipara (Keough & Dartnall, 1978) and P. vivipara (Dartnall, 1969) are Australian small range endemic seastars occurring on coasts of western Eyre Peninsula (South Australia) and southeast Tasmania, respectively
Liversage K, Byrne M sponges and other encrusters as well as anoxia
Parvulastra parvivipara (Keough & Dartnall, 1978) and P. vivipara (Dartnall, 1969) are Australian small range endemic seastars occurring on coasts of western Eyre Peninsula (South Australia) and southeast Tasmania, respectively
Summary
Parvulastra parvivipara (Keough & Dartnall, 1978) and P. vivipara (Dartnall, 1969) are Australian small range endemic seastars occurring on coasts of western Eyre Peninsula (South Australia) and southeast Tasmania, respectively. Both species have atypical lifehistories involving a diminutive size, simultaneous hermaphroditism, almost exclusive selffertilisation, and brooding offspring in the gonads to an advanced juvenile which is achieved by sibling cannibalism (Byrne 1996). Adult P. parvivipara are among the world’s smallest seastars reaching a diameter of only 11 mm while P. vivipara are slightly larger Both species have extreme poverty of genetic diversity (Keever et al 2013). During night they emerge from under boulders (Prestedge 1998, Roediger and Bolton 2008) to graze on microalgae similar to the much studied P. exigua (Martinez et al 2016)
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