Document: SAR-3-46-10

Functional-morphological trade-offs in an African Cyprinid: Implications for faunal diversification.

SCHAACK, S.* and L.J.CHAPMAN

University of Florida, Gainesville, FL 32611, USA ¹

Abstract:
Adaptive change in one character may affect a second, non-functionally related character in an adaptive or non-adaptive way. For example, in some species, fish living in low oxygen environments have larger gills than conspecifics living in normoxic or high oxygen water. This may alter feeding structures and therefore have indirect effects on other fitness components. This study investigates whether adaptive variation in gill size of the African cyprinid Barbus neumayeri constrains associated trophic structures and affects foraging ecology and fitness-related characters among populations. Barbus neumayeri from the dense interior of a papyrus swamp have much larger gills than fish from connected streams where oxygen levels are high. Reciprocal transplant experiments showed lower survivorship for small-gilled fish when placed in hypoxic swamp waters, indicating large-gilled fish in the swamp may be demonstrating an adaptive response. Although there is no apparent survivorship cost to large gills in high oxygen, these fish may suffer a competitive disadvantage if their large gills impact associated feeding structures. We compared the trophic morphology and feeding ability of fish from small- and large-gilled populations. Fish from the two habitats differed significantly in both external measurements and the structural elements surrounding the gills. This rearrangement of muscles in the large-gilled fish suggests a reduction in biting capacity. In paired feeding trials, large-gilled fish spent more time feeding than small-gilled fish of the same body size, without ingesting more food. These results suggest less efficient food intake in large-gilled fish. Field data (length-weight measurements) from the different populations showed lower condition in swamp-dwelling fish that may reflect the observed differences in prey availability and diet, hypoxia stress, or less efficient feeding behavior. We argue that variation in gill size has facilitated the broad habitat distribution of Barbus neumayeri. However, gill size and changes in associated structures may limit the success of phenotypes crossing physico-chemical gradients and lead to to diversification in this species.

Keywords: intraspecific variation, Barbus, feeding performance, foraging ecology, hypoxia, papyrus swamps

This abstract is being presented at: 2:30 PM in session:
Oral Session #62: Freshwater Fish Ecology.