ADAPTIVE COLORATION AND GENE FLOW AS A CONSTRAINT TO LOCAL ADAPTATION IN THE STREAMSIDE SALAMANDER, AMBYSTOMA BARBOURI

Abstract

Predation is an important selective force that influences animal color patterns. Some larval populations of the streamside salamander, Ambystoma barbouri, inhabit streams with fish predators. Other larval salamanders are found in shallow, ephemeral streams that are predator-free. Quantitative melanophore cell counts and estimates of percent body area pigmented indicated that larval coloration is strongly correlated with stream type. Larvae that coexist with fish tend to be lighter than larvae from streams that are Ashless and ephemeral. Two approaches demonstrated that lightly pigmented salamander larvae better match the common background in relatively permanent streams and are less conspicuous to fish than dark larvae. First, using a model based on the spectral sensitivity of the fish and reflectance properties of salamanders and natural stream backgrounds, we showed that light larvae are three times more cryptic than dark larvae on rocks. Second, lighter larvae had higher survival than darker salamanders on rocks in a predator- choice experiment. It is not clear why larvae in ephemeral streams are darker. Larvae in ephemeral streams should be active to feed and develop rapidly and reach sufficient size to metamorphose before seasonal drying. Several hypotheses may explain why larvae tend to be darker in ephemeral streams, such as increased thermoregulatory ability, better screening of ultraviolet radiation (in these shallower streams), or better background matching to terrestrial predators. Among populations where salamander larvae coexist with fish, there are differences in relative crypsis. Larvae from populations with fish and relatively high gene flow from ephemeral populations (where larvae are dark) tend to be darker (with more melanophores) and more conspicuous to predators than those from more genetically isolated populations, where larvae are lighter and more cryptic. These differences illustrate the role of gene flow as a constraint to adaptive evolution.

Reproductive Isolation Between Divergent Races of Pea Aphids on Two Hosts. Ii. Selection Against Migrants and Hybrids in the Parental Environments

“…The evolution of local adaptation can clearly be constrained by gene flow from populations that have been selected in different environments (e.g., Storfer et al 1999). If divergent selection is strong enough, however, it can overcome the effects of free movement between environments by eliminating migrants from other environments before they have an opportunity to mate or by disfavoring the hybrids that are produced by such matings.…”

Evolution of Color Variation in Dragon Lizards: Quantitative Tests of the Role of Crypsis and Local Adaptation

“…Although there is now a large body of empirical and comparative evidence to support the hypothesis that variation in the strength of sexual selection can lead to differences in coloration between the sexes and between populations (e.g., Hill 1994;Endler and Houde 1995;Baird et al 1997;Bennett and Owens 2002;Kwiatkowski and Sullivan 2002), quantitative studies on the relative role of crypsis are comparatively rare (but see Endler 1984;Merilaita 1998;Storfer et al 1999). In addition, most previous studies of crypsis have relied on human-oriented indices (e.g., Steward 1977;Gotmark 1993;Gotmark and Hohlfalt 1995) or estimates of color contrast that do not consider the receiver's visual system (e.g., Majerus et al 2000;Macedonia 2001;Macedonia et al 2002;Heindl and Winkler 2003).…”

“…Using this model it is possible to calculate objective measures of chromatic (''hue'') and achromatic (''brightness'') contrast of animal color patterns against natural backgrounds as viewed by the receiver's visual system under natural illumination Stuart-Fox et al 2003). So far, such receiver-relative measures of contrast have only been used to make qualitative statements about colors appearing more or less conspicuous to a receiver (e.g., Storfer et al 1999;Marshall 2000;StuartFox et al 2003). Here, we extend the use of such measures to a quantitative examination of variation in crypsis and conspicuousness, as perceived by a predator.…”

Risky prey behavior evolves in risky habitats

“…19). When gene flow is limited by physical barriers or isolation by distance, prey foraging rate is expected to evolve to match the specific predation and environmental contexts of each population (9,20,21). The degree to which a population is adapted or maladapted to its habitat often depends on selection intensity and gene flow (22)(23)(24).…”