Document: WIL-3-46-19

You CAN take it with you: Colonization success and population structure of female- and pair- founded populations of Gambusia affinis.

RESETARITS, JR., W.J.*

Old Dominion University, Norfolk, VA 23529, USA ¹

Abstract:
Many theories have been proposed to explain the evolution and maintenance of sexual reproduction. A common thread is the presumed fitness advantage accrued to parents producing more genetically diverse progeny. This advantage must overcome the reproductive efficiency of asexual reproduction. Among vertebrates, where sexual reproduction predominates, parthenogenesis is found in a very few taxa and correlated with environmental conditions, particularly disturbance, where its reproductive advantage confers an even greater advantage for (re)colonization. While parthenogenesis is rare in vertebrates, certain species display life histories that presumably obtain some of the same advantages, while maintaining the genetic diversity of sexual reproduction. Female mosquitofish, Gambusia affinis, store sperm from one or more males and use that sperm to fertilize susequent broods. This presumably allows a female in a natural population to be a foundress any time after sexual maturity. Several basic questions arise in regard to this life history; What percentage of mature females in nature can successfully found populations at any given time, and does this differ from the success rate of pairs from the same population? Do populations founded by females differ in growth rate and population structure from those founded by male/female pairs? I introduced G. affinis into 24 experimental mesocosms, 12 receiving a single mature female and 12 male/female pairs. There was no difference in founding success rate for females (83%) vs pairs (75%). After seven weeks populations consisted, on average, of 5.0 males, 7.5 females, 31.9 fry, and 117.7 eggs and eyed embryos. Numbers of males, females, immatures, embryos, and eggs did not differ between female-founded and pair- founded populations, nor did average size of males, females and fry. A significant effect of foundress final size on the number of immatures, embryos and eggs produced was the only significant observed relationship. Internal fertilization and sperm storage allows mature females the colonization advantage of parthenogens, while maintaining the advantages of sexual reproduction. Individual females were as successful in founding populations as pairs, and populations founded by females were indistinguishable from those founded by pairs.

Keywords: reproduction, colonization, foundress, population, sexual, asexual, Gambusia

This abstract is being presented at: 2:15 PM in session:
Oral Session #62: Freshwater Fish Ecology.