Self-Fertilization and the Role of Males in Populations of Tadpole Shrimp (Branchiopoda: Notostraca: Triops)

Abstract

Self-fertilization has both negative and positive fitness effects on species evolution. Selfing can increase inbreeding depression, thereby decreasing genetic diversity. In contrast, self-fertilization can preserve beneficial gene combinations and facilitate colonization success. Within the class of crustaceans Branchiopoda, selfing is a primary reproductive mode. Some species of Triops, in the family Notostraca, are a few of the animal species thought to have a mixed mating system between hermaphrodites and males termed androdioecy. The objective of this study is to validate the reproductive mode utilized by Triops newberryi in southern New Mexico by the use of progeny arrays and population simulations. Individuals were reared in the lab from dried soil collected from temporary ponds inhabited by T. newberryi The adults reared and the encysted embryos contained within their brood pouches were genotyped using 7 T. newberryi specific microsatellite markers to determine the relatedness between parent and offspring. Overall microsatellite diversity was low with few heterozygous individuals and limited polymorphisms. Simulated populations and allele segregation analysis suggest hermaphroditism is the primary reproductive mode for T. newberryi In addition, based on the offspring's alleles, there was no direct evidence that a male (ovisacless) T. newberryi outcrossed with a female. Population simulations further suggest that the rate of successful outcrossing events must be low and could explain why outcrossing was not observed in the laboratory rearing trials.

Keywords: androdioecy; hermaphrodite; microsatellites; parthenogenesis; progeny array.