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Introgression in Pupfish

A. The role of sexual and natural selection in the rapid establishment and persistence of a hybrid swarm between the native New Mexican Pecos Pupfish (Cyprinodon pecosensis) and the sheepshead minnow (C. variegatus). A preference of Pecos pupfish females for sheepshead minnow males provided the initial impetus for hybridization and introgression. The enhanced fitness of hybrids, especially over the native Pecos pupfish, maintains the hybrid swarm and facilitates expansion beyond the historic range of the Pecos pupfish.

B. Introgression between native pupfish (C. peconsensis, C. elegans) and an exotic congener, the sheepshead minnow (C. variegatus). A comparative study mapping the development of premating and postmating isolating mechanisms onto a phylogeny of this group.

Bottomless Lake
Mirror Lake at Bottomless Lakes State Park
Bitter Lake
Bitter Lakes Wildlife Refuge
Habitats of Pecos pupfish in New Mexico

Sympatric Speciation in Pupfish

The process of speciation in a species flock of pupfish in lake Chichancanab, Mexico. We are particularly interested in the evolution of olfactory and visual premating isolating mechanisms in this group of pupfish. The five species are morphologically distinct, especially in the structure of their mouthparts, suggesting trophic differentiation. The flock is young (less than 8,000 years) and only one of the five putative species (C. maya) has genetically differentiated.

C. labiosus
(Invertebrate feeder)
C. maya
C. beltrani
Pupfishes in Lake Chichancanab, Mexico

Sexual selection in guppies

A. Female choice of multiple male traits. The relative importance of male color, especially carotenoids, and courtship behavior in female choice was investigated using synthetic animations of male guppies. Females based their preference for male images primarily on dynamic traits (courtship), and only secondarily on static traits (color).

B. Changes in female choice with age and mating experience. Video tapes of males, differing in the area of carotenoid color spots, were used to asses the effect of age and mating experience on female preference for ornamental males. Female choice changed with age but not with mating experience.

C. Manipulation of male appearance with ultraviolet (UV) transmitting and UV blocking filters indicates that females respond to UV reflective color patterns, and these may enhance male mating success. Since cichlid predators of guppies lack UV sensitive cones, UV reflective patterns function as 'private wavelengths' and should be particularly important in enhancing male attractiveness in environments with predators.

Ultraviolet refletive color patterns in guppy males enhance their attractiveness to females. Guppi

Allometry of ornaments and weapon

Exaggerated male traits that have evolved under sexual selection include ornaments to attract mates and weapons to deter rivals. Data from studies of many such traits in diverse kinds of organisms show that they almost universally exhibit positive allometries. Both ornaments and weapons increase disproportionately with overall body size, resulting in scaling exponents within species that are consistently greater than 1.0 and can be as high as 5. A simple mathematical model of resource allocation during ontogeny shows that scaling exponents reflect the relative fitness advantages of ornaments vs. somatic growth. Since the scaling exponents are similar for different taxonomic groups, it follows that the fitness advantages of investing in ornaments are also similar. The model also shows how selection for ornaments influences body size at first reproduction and explains why interspecific allometries have consistently lower exponents than intraspecific ones.

Allometry Figure


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