1 INTRODUCTION
The
impact of ambient temperature on animal
physiology
, behavior , and life history traits , is well-established. However, the
underlying mechanisms of how ambient temperature influences sexual
selection, which is a key evolutionary force shaping reproductive traits
and behaviors , remain unclear . The cost-benefit balance of sexual
selection could be influenced by ambient temperature, which can impact
the growth and maintenance of sexual weapons or ornaments , alter
intrasexual competition and intersexual selection , influence the
variance in reproductive success , and even impact mating systems .
Furthermore, the cost-benefit balance of bearing
ornamentation
may be more significant than that of possessing weapons, as
ornamentations often have limited direct benefits. Thus, understanding
how ambient temperature influences preference for secondary sexually
selected traits could have significant implications for understanding of
animal behavior evolution and species adaptation to changing
environmental
conditions.
Due
to the restricted resource expenditure and predation risks, male
ornament characteristics are known to be costly to develop and maintain
. Reduced sexual dimorphism has been linked to lower ambient
temperatures, which may restrict the aesthetic expression of male
ornamentation . Additionally, it has been demonstrated that the
trade-off between immunological function and plumage expression for
carotenoid-based decorations acts as a sexual cue for the quality of a
particular bird . Additionally, according to experimental data, male
zebra finches (Taeniopygia guttata ) tend to circulate more
carotenoids in cooler climates rather than expressing them as
carotenoid-based decorations . This points to a potential problem with
the use of carotenoid-based decorations as accurate indicators of an
individual’s character in colder climates.
Ambient temperature can impact animal courtship behavior in addition to
influencing the display of sexual characteristics. Several studies have
shown that male courting efforts are positively correlated with
temperature . This suggests that males with low resource investment
engage in intensive courting behavior. This might be because they have
more energy to devote to mating displays or are more driven to locate
partners. Additionally, ectothermic and endothermic animals’ metabolism
and activity levels are greatly influenced by ambient temperature .
These factors can also affect how much time these animals devote to
mating and intrasexual competition .
Furthermore, ambient temperature can affect a female’s post-copulatory
mate preference and even a species’ mating system. Parental care efforts
needed significant inputs by patents as the environmental conditions
became harsher, requiring longer incubation durations and intensive nest
provisioning . Females in colder environments may be unable to
compensate for these shortages, and instead pursue less-ornamented males
with higher levels of direct parental investment because males with
extravagant ornaments often provide limited parental care .
Additionally, the increased necessity for parental care by both parents
in colder environments may promote stable pair-bond and thus the
evolution of biparental care. This transition to monogamy can be viewed
as an adaptive strategy to better manage balanced parental investment
and assure the survival of offspring in challenging environmental
circumstances.
Shorebirds provide an ideal system within which to test the impacts of
ambient temperature on mate choice. This is because shorebirds can be
found breeding in a wide variety of wetland habitats across large
temperature gradients, even on the intraspecific level. Specifically, we
used four Charadrius plover populations from the Kentish plover
(C. alexandrinus ) species complex which breed in locations with
significant changes in ambient temperature throughout the mating season
(Figure 1 and Song et al. 2020). Our study included three populations of
Kentish plovers (C. alexandrinussensu stricto) and one population of
white-faced plovers (C. dealbatus ), a former subspecies ofCharadrius alexandrinus that has recently been proven to be a
full species that diverged from the former less than 600 000 years ago .
The goal of this study was to look at the effect of ambient temperature
on male ornamentation, female mate choice, and parental investment
across diverse populations. We specifically investigated if male
ornamentation expression and its relationship to body size change with
ambient temperature. Furthermore, we investigated how female mate choice
at different temperatures responds to male ornamentation by assessing
the connection between morphometric and ornament characteristics of
males and females in mating pairings. Finally, we investigated whether
female incubation investment is related to male ornamentation and if it
varies with temperature. Our prediction is that under colder conditions,
the trade-off between color expression and immune function on melanin
and/or carotenoid may lead to a lower correlation between ornament and
body size. Females may also prefer larger males with direct parental
care over ornamented males with lower parental care, due to the
increased need for parental investment in colder environments.