ABSTRACT
Among vertebrates, shes show the greatest biological, morphological, and ecological diversity, which is reected in the variety of their reproductive strategies. Within this group, Cyprinodontiformes have developed unique reproductive strategies and, among Neotropical groups, the family Rivulidae stands out because it includes species with annual life cycles. This is the case of the genus Austrolebias, with 39 currently recognized species (Loureiro et al., 2011). This genus inhabits temporal ponds in Paraguay, Uruguay (Figure 3.1), southern Brazil, and reaching into north and northeast Argentina (Costa, 2006; Loureiro et al., 2011). Like other rivulids, Austrolebias has external fertilization, and the male gamete has remarkable morphological adaptations, including changes in size, shape, and ultrastructure that are probably related to fertilization efciency.
