Sc. Woolley et al., Evolutionary changes in dopaminergic modulation of courtship behavior in Cnemidophorus whiptail lizards, HORMONE BEH, 40(4), 2001, pp. 483-489
Preoptic dopamine release is integral to the display of copulatory behavior
s in male mammals and birds. However, while the anatomical distributions of
the dopamine synthesizing enzyme tyrosine hydroxylase are similar among ve
rtebrates, evolutionary changes in the functional role of dopamine are poor
ly understood. In this study, we tested whether a dopamine D1 receptor agon
ist would facilitate the display of courtship and copulatory behaviors in t
wo related Cnemidophorine lizards (Cnemidophorus inornatus and Cnemidophoru
s uniparens). Cnemidophorus lizards offer a unique system to study evolutio
nary changes in functionality because ancestral (e.g., C. inornatus) and de
scendant (e.g., C. uniparens) species can be studied in parallel. Cnemidoph
orus uniparens is an all-female, parthenogenetic species and is the triploi
d descendant of the sexual and diploid species C. inornatus. Here we report
that in castrated male C. inornatus and ovariectomized C. uniparens a dopa
mine D1 agonist increased the proportion of individuals mounting and decrea
sed the latency to mount. Moreover, there was a species difference in sensi
tivity to the agonist: Mounting was elicited at a lower dose in C. uniparen
s than in C. inornatus, One possible explanation for this heightened sensit
ivity in the triploid parthenogen is that, by virtue of the increased ploid
y, the parthenogen has elevated levels of DI receptor in limbic brain areas
modulating courtship behavior. (C) 2001 Elsevier Science.