Polymorphism in Developmental Mode and Its Effect on Population Genetic Structure of a Spionid Polychaete, Pygospio elegans

Abstract

Population genetic structure of sedentary marine species is expected to be shaped mainly by the dispersal ability of their larvae. Long-lived planktonic larvae can connect populations through migration and gene flow, whereas species with nondispersive benthic or direct-developing larvae are expected to have genetically differentiated populations. Poecilogonous species producing different larval types are ideal when studying the effect of developmental mode on population genetic structure and connectivity. In the spionid polychaete Pygospio elegans, different larval types have been observed between, and sometimes also within, populations. We used microsatellite markers to study population structure of European P. elegans from the Baltic Sea (BS) and North Sea (NS). We found that populations with planktonic larvae had higher genetic diversity than did populations with benthic larvae. However, this pattern may not be related to developmental mode, since in P. elegans, developmental mode may be associated with geography. Benthic larvae were more commonly seen in the brackish BS and planktonic larvae were predominant in the NS, although both larval types also are found from both areas. Significant isolation-by-distance (IBD) was found overall and within regions. Most of the pair-wise F(ST) comparisons among populations were significant, although some geographically close populations with planktonic larvae were found to be genetically similar. However, these results, together with the pattern of IBD, autocorrelation within populations, as well as high estimated local recruitment, suggest that dispersal is limited in populations with planktonic larvae as well as in those with benthic larvae. The decrease in salinity between the NS and BS causes a barrier to gene flow in many marine species. In P. elegans, low, but significant, differentiation was detected between the NS and BS (3.34% in AMOVA), but no clear transition zone was observed, indicating that larvae are not hampered by the change in salinity.

Temporal genetic structure in a poecilogonous polychaete: the interplay of developmental mode and environmental stochasticity

“…For example, even in the exposed sand flat population in UK, local currents may facilitate larval retention [40]. Continuous high local larval retention could lead to the spatial genetic structure pattern seen in P. elegans (shown here and in [42]), as well as to the high F IS values observed in these populations. Recent studies have shown that local larval recruitment in the marine habitat may be more common than assumed [4,85,86].…”

“…In some populations multiple larval types have been observed simultaneously or seasonally [35,36,42], but many populations of P. elegans are known to produce only one larval type (e.g. [34,40,46]).…”

De novo transcriptome assembly and developmental mode specific gene expression of Pygospio elegans

“…P. elegans has been described as opportunistic and it can be found in many different habitats with different salinities and temperatures, but it thrives in sandy intertidal mud flats (Anger, 1984;Kesäniemi, Geuverink, & Knott, 2012;Morgan, 1997). P. elegans has been described as opportunistic and it can be found in many different habitats with different salinities and temperatures, but it thrives in sandy intertidal mud flats (Anger, 1984;Kesäniemi, Geuverink, & Knott, 2012;Morgan, 1997).…”

“…P. elegans exhibits polymorphism in its reproductive and developmental strategies (Kesäniemi et al, 2012;Rasmussen, 1953Rasmussen, , 1973). Females can produce either a small number of benthic larvae that are brooded in the egg capsules throughout their development (these larvae lack a dispersive, freeswimming stage), or females can produce a large number of planktonic larvae that are only briefly brooded before they emerge from the egg capsules to complete their development in the plankton (see details in Kesäniemi et al, 2012;Thonig, Banta, Winding Hansen, & Knott, 2016). After internal fertilization, females lay embryos into egg capsules inside the maternal tube where the larvae are brooded.…”

Hox gene expression during postlarval development of the polychaete Alitta virens

“…Sometimes within a single family (such as Nereididae), there are species that have all stages of development from trochophore to an adult segmented worm ( Platynereis dumerilii ), as well as species with direct development ( Neanthes arenaceodentata ) [10,13,14]. Finally, different individuals of the same species can have direct development as well as development through a larval stage; moreover, the larvae can be of different types (planktonic and benthic) [15,16]. …”