Diapausing egg banks, lake size, and genetic diversity in the rotifer Brachionus plicatilis M\xfcller (Rotifera, Monogononta)

Javier Montero-Pau,Africa Gómez,Manuel Serra

doi:10.1007/s10750-016-2833-4

Abstract

Diapausing egg banks are reservoirs of ecological and genetic diversity in continental zooplankton. However, although habitat size has often been used as a proxy for population size, the relationship between diapausing egg bank size and genetic diversity has not been explicitly tested in zooplankton. We estimated the density and size of diapausing egg banks, habitat size and genetic diversity (for mitochondrial and nuclear markers) of 14 populations of the rotifer Brachionus plicatilis in an endorheic basin in the SE Iberian Peninsula. The size of B. plicatilis diapausing egg banks ranged across eight orders of magnitude (from 257 to 4.9 × 1010 eggs). Despite the small geographical scale, populations were strongly structured genetically, but with no evidence of isolation by distance. Habitat size (lake area) was a better predictor of genetic diversity than total diapausing egg bank size, but only for mtDNA haplotype diversity. However, as these results were driven by the strong effect of the largest lake in the database, they should be taken with caution. Our results suggest that large lakes could have a disproportionate effect on genetic diversity and that more work is needed to support the use of habitat size as a proxy of population size in rotifers.

Highlights

Most groups of continental zooplankton produce egg banks, accumulations of large numbers of diapausing eggs analogous to annual plant seed banks (Brendonck & De Meester, 2003)
Species identification of the specimens of the species complex based on 16S haplotypes shows that B. plicatilis s. s. was found in all 14 lakes, while B. manjavacas, the more common species, was found in seven lakes, mainly in the central samples, with 2–56% of the total eggs analyzed (Tables 1, 2)
Our results suggest that lake area is a better predictor of population genetic diversity than the size of B. plicatilis s. s. diapausing egg banks, this effect was only significant when population genetic diversity was estimated for mtDNA, but not for nuclear DNA, and was due to a disproportionate effect of the largest lake Petrola

Summary

Introduction

Most groups of continental zooplankton produce egg banks, accumulations of large numbers of diapausing eggs analogous to annual plant seed banks (Brendonck & De Meester, 2003). Diapausing egg banks are reservoirs of both neutral and adaptive genetic variation, and function as a population memory of past selective conditions (Cousyn et al, 2001) Of crucial importance, they allow population survival during adverse periods and can facilitate species coexistence (Caceres, 1997; Montero-Pau et al, 2011). From a metapopulation perspective approach, large populations could serve as propagule sources for small populations, which in turn would act as genetic sinks more prone to extinction/recolonization cycles. Both genetic and demographic effects should contribute to a positive association between population size and genetic diversity. The relationship between population size and genetic diversity has not been explicitly tested in zooplankton

Methods

Results

Conclusion