Biology ETDs

Publication Date



The Pecos Gambusia, Gambusia nobilis, is an endangered, live bearing fish inhabiting sinkholes in a restricted range of the Pecos River Watershed in New Mexico and Texas. The sink holes at Bitter Lake National Wildlife Refuge (BLNWR), Roswell, NM create isolated habitats with varying ecological conditions (habitat size, community composition, dissolved oxygen, salinity and pH). This ecological variation imposes unique selective pressures that may shape differences in life history characteristics and morphology between populations. The goals of this research were to characterize seasonal and population variation in 1) life history characteristics, 2) embryo development patterns, 3) morphology and 4) explore cursory relationships between ecological conditions and G. nobilis morphology and life history. Monthly sampling was conducted at BLNWR (May 2011 through April 2012) at sinkholes 7, 27 South, 31, and 37. A trade-off between egg size and brood size was observed from investment in many small embryos to fewer large offspring from April through August. Despite differences in ecological parameters, no significant differences in reproductive traits were observed between the populations. Interestingly, reproductive effort and average egg size were not correlated with female size. Larger females invested relatively the same amount into reproduction but invested in larger broods rather than increased average egg mass. An analysis of embryo developmental stages identified 1) asynchronous reproduction between females, 2) eggs in multiple stages of development within some gravid females (evidence for superfetation), and 3) increasing average egg mass of later developmental stages suggesting some element of matrotrophy (post-fertilization nutrient transfer). Geometric morphometric techniques were used to evaluate seasonal and population shape differences. During the reproductive season, females tended to be deeper bodied with a posteriorly shifted anal fin. Males and females from sinkhole 31 differed significantly from the other populations; they had deeper body profiles and shorter caudal peduncles than sinkholes 7, 27 South, and 37 which could be related to less predation and higher dissolved oxygen in sinkhole 31. Analyzing life history allocation strategies and identifying seasonal and population differences in morphology and reproduction contributes information that may be important in formulating management strategies and conservation plans for this endangered species.




Gambusia, Life history, Morphometrics, Embryo, Reproduction, Ecology

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Advisor

Kodric-Brown, Astrid

First Committee Member (Chair)

Turner, Thomas

Second Committee Member

Wolf, Blair