Dispensable and indispensable genes in an ameiotic fish, the Amazon molly <i>Poecilia formosa</i>

Abstract

All-female vertebrates are excellent model systems for studying many evolutionary problems. One of these is the Amazon molly. In this review, three aspects of its biology are discussed: (1) An important question is how dispensable genes, such as all male coding genes, evolve in this species. A number of studies found that most of these genes remain remarkably stable and functional. (2) The gynogenetic Amazon mollies have to live in sympatry with males of a gonochoristic species, because sperm are needed to trigger embryogenesis. Yet, Amazon mollies cannot replace their sexual competitors, because this would lead to their own extinction. Studies on the behavior of Amazon mollies and their sperm-donor species indicate that a number of behavior patterns stabilize the mating system by providing Amazon mollies with the copulations they need to reproduce. (3) The age of Amazon mollies has been estimated to be approximately 100,000 years. This is older than predicted by some theoretical models. In Amazon mollies two ways to occasionally incorporate fresh genetic material have evolved. One way is to add one complete set of paternal chromosomes, which, in nature, leads to stable triploid lineages. The second way is the incorporation of minute, centromere-containing microchromosomes. The evolutionary impact of these phenomena, however, is not resolved so far and needs further study.

Peering Through the Looking Glass at a Sexual Parasite: Are Amazon Mollies Red Queens?

“…The power of the statistical analyses used here may be lacking because sample sizes are relatively small. However, numerous studies have documented significant differences in these behaviors in these fishes using similar experimental protocols, sample sizes, and rank statistics (Schlupp et al 1991(Schlupp et al , 1994(Schlupp et al , 1998Foran and Ryan 1994;Ryan et al 1996, Ptacek and Travis 1997Schlupp and Ryan 1997;Kö rner et al 1999;Landmann et al 1999). This suggests that the similarity in male response to hybrid and gynogenetic females in this study is not an anomaly, but rather is consistent with male behavior observed in other studies for these two species.…”

“…Based on this imperfection, some studies have concluded that the evolutionary persistence of gynogenetic P. formosa is the result of a host/parasite coevolutionary arms race (Schlupp et al 1991(Schlupp et al , 1994Schartl et al 1995b;Schlupp and Ryan 1997). In this context, attractiveness of gynogenetic females imposes selection on heterospecific males, favoring the evolution of stronger male mate discrimination that, in turn, imposes selection on the gynogenetic females to evolve an even greater ability to attract males (Schlupp et al 1991;Schlupp and Ryan 1996;Schlupp et al 1998). Hence, gynogenetic females have been dubbed ''Red Queens'' (Schlupp et al 1991) because they may be locked in a coevolutionary battle with heterospecific males to maintain their ability to obtain sperm.…”

How populations persist when asexuality requires sex: the spatial dynamics of coping with sperm parasites

“…However, this may be a difficult argument to apply for many gynogenetic species complexes. The asexual and sexual species need to be very close relatives for sperm to trigger embryogenesis properly (Hubbs & Hubbs 1932;Schlupp et al 1998), and speciation in this case is argued to reflect a single hybridization event ( Turner 1982;Avise et al 1991;Schartl et al 1995) rather than a process of niche differentiation. There is also currently neither evidence of niche differentiation (Heubel 2004) nor differences in reproductive rates in the same environment (Schlupp 2005).…”

Differential screening and characterization analysis of the egg envelope glycoprotein ZP3 cDNAs between gynogenetic and gonochoristic crucian carp

“…As similar to other gynogenetic fishes [43][44][45], the triploid gynoform was also demonstrated to be originated from an ancient hybridization event, and the maternal and paternal species might be Carassius auratus and Cyprinus carpio respectively [46]. In comparison with gonochoristic crucian carp, the major difference between them is the mode of reproduction.…”