Martin, J and P Lopez. 2008. Female sensory bias may allow honest chemical signaling by male Iberian rock lizards. Behav Ecol Sociobiol. 62-1927-1934

Researchers studied the evolution of chemosensory signals in Iberian rock lizards (Iberolacerta cyreni). Researchers state that some signaling theories propose that only honest signals may be evolutionarily stable, a concept introduced in lecture. Initially the Iberian rock lizards may appear to be taking advantage of sensory bias of females towards cholesta-5,7-den-3-ol (provitamin D₃) that is a precursor to vitamin D₃, an important vitamin produced in the skin but supplemented in food. Male lizards of this species produce femoral gland secretions that include fatty acids, alcohols and steroids (including provitamin D₃) thus it appears males are exploiting on sensory bias. Provitamin D₃ in femoral secretions is believed to be an honest indicator of male quality. Researchers studied whether females had a preexisting bias to this chemical that males began exploiting more recently. They theorized that if the female chemosensory attraction to provitamin D₃ increased with hunger it would indicate a preexisting attraction to food chemicals.

Iberian rock lizards were captured and half of the females were fed (control) and the other half were not fed for five days. Tongue flick (TF) rates change were used to determine female attraction to two sets of chemical stimuli: femoral gland scents, mealworm scent, and deionized water or cholesterol, provitamin D₃ and dichloromethane (DMC). In a second experiment male scents were collected on absorbent strips, provitamin D₃ levels were manipulated, the strips were placed on opposite ends of cages and time spent by females on each strip was measured.

Hungry females had more TF’s than control females to both mealworm and male scents in the first set of odors and both cholesterol and provitamin D₃ in the second. Hungry females spent significantly more time on paper strips with added provitamin D₃ than paper strips that had not been supplemented, this difference was not significant for control females. Food-deprived females had a greater response to provitamin D₃ than control females. Results suggest hungry females are more attracted to provitamin D₃ in male scents. The researchers assert that these results support the conclusion that males are exploiting a preexisting sensory bias in females for food-associated chemicals. The researchers conclude that sensory bias can be exploited by males in an honest manner and that these models are not mutually exclusive.

The concepts of honest signals and sensory bias were major themes in this paper. Female Iberian rock lizards appear to be attracted to provitamin D₃ found both in food and male femoral secretions males much like female guppies prefer orange foods and orange males. The difference between this study and those discussed in class is that instead of visual signals the female lizards are attracted to chemical odors. In class we discussed different ideas about signal honesty including the arms race concept where much signaling is deceitful and the theory that signals must be costly in order to be honest. It appears that what initially seemed to be a deceitful signal may actually fit the model of honest signaling even as it exploits a sensory bias. The question of which came first, signal or perception was addressed in class and in this paper. The authors argue that perception occurred first in these lizards. We also discussed types of signal and receiver precursors in class. Provitamin D₃ appears to be a dietary type of signal precursor that was likely present in the diet before it began to be secreted by male femoral glands. On the receiver side, a sensory bias for the provitamin D₃ food chemical seems to be a receiver precursor. Researchers cite unpublished data indicating that males of the closely related species I. monticola do not have provitamin D₃ in femoral secretions yet females are still attracted to this scent in food. This observation is the beginning of a comparative analysis of signal evolution such as was mentioned in lecture. The comparison to I. monticola suggests that a wider phylogenetic analysis of multiple different species could provide another test of whether signal or perception occurred first.