Browsing by Subject "Sexual selection in animals"

Now showing 1 - 5 of 5

Evolution of ecomorphological variation and acoustic diversity in mate-recognition signals of Southeast Asian forest frogs (subfamily Platymantinae)
(2004-05) Brown, Rafe Marion, 1968-; Cannatella, David C.; Hillis, David M., 1958-
Female mate choice for socially variable advertisement calls in the cricket frog, Acris crepitans
(2001-08) Kime, Nicole Marie, 1970-; Ryan, Michael J. (Michael Joseph), 1953-
Male cricket frogs produce a single call-type, the advertisement call. In interactions with neighboring males, they decrease the dominant frequency and increase the temporal complexity of these calls. It was previously suggested that vocal escalation mediates male-male aggression. This is likely true for spectral call changes, but a review of previous data on male vocal and territorial behavior does not clearly support this hypothesis for temporal call characters. One alternative is that males change their calls in order to increase their relative attractiveness to females. I conducted a series of phonotaxis experiments assessing female responses to socially variable call characters. Female cricket frogs prefer calls with the temporal patterning of interacting males to those with the temporal patterning of undisturbed males, and mean to variant dominant frequencies. I suggest that vocal escalation by male cricket frogs reflects a tradeoff between the benefits of increased attractiveness to females and the costs of attractive calls in other contexts. Some of the observed preferences for complex calls may be influenced by neural processes that are not specific to female cricket frogs, but that are general among species. Females prefer calls that are partitioned into multiple pulse groups. This preference may result from a release of adaptation or habituation to long calls. Females discriminate preferentially with respect to calls nearer the end of calling bouts. I suggest that cognitive constraints on call processing may limit the number of calls to which females can attend in mate choice. Males appear to be sensitive to this limitation, as vocal escalation occurs only for calls near the end of bouts. Although female cricket frogs prefer complex calls, there is no evidence that advertisement call complexity enhances their ability to detect, recognize, or localize males in noisy choruses. In cricket frogs, in fact, complex calls may carry a cost with respect to signal localization. Thus, while vocal escalation increases a male’s relative attractiveness to females, there is currently no evidence to suggest that facultative increases in call complexity address the particular problems of signal detection and localization in a noisy environment.
Hormonal mechanisms for variation in female mate choice
(2005) Lynch, Kathleen Sheila; Wilczyński, W.
Although female mate choice has been the subject of many investigations, the causes of variation in mate choice are less understood. Theoretical models predict that individual females should show variable mate choices as a consequence of intrinsic and extrinsic factors. Empirical support for these predictions demonstrates that females show flexible mate choices over their lifetime, the breeding season and a reproductive cycle. The objective of the research presented here is to examine two intrinsic factors, reproductive and hormonal state, to determine how these contribute to individual variation in female mate choice over a reproductive cycle. I examine the link between flexibility in mate choice behavior, changes in gonadal hormones and hormonal modulation of sensory systems involved in mate choice behavior. Flexibility in mate choice was examined in female túngara frogs (Physalaemus pustulosus), a Neotropical species in which mate choice has been well studied. Acoustic based phonotaxis tests were used to assay mate choice behaviors such as receptivity, permissiveness and discrimination. These behaviors are respectively defined as a response to conspecific mate signals, a response to unattractive mate signals and the ability to discern the v difference between mate signals. The expression of receptive and permissive mate choices significantly fluctuates throughout different reproductive stages. The concentration of gonadal steroids, such as estrogen, progesterone and androgens, also significantly fluctuate throughout the same reproductive stages. Furthermore, hormone concentration was manipulated using human chorionic gonadotropin (HCG) and such manipulation induces flexible mate choice. Finally, I investigate whether hormones modulate a central auditory nucleus involved in phonotaxis behavior. Immediate early gene (IEG) induction, specifically egr-1, was used to mark neuron activity. Females were treated with either HCG or saline and exposed to either mate choruses or silence. Egr-1 expression was quantified in an auditory midbrain nucleus, the torus semicircularis (TS). The region within the TS responsible for auditory-motor integration showed a near significant elevation in egr-1 expression in response to acoustic exposure and a significant elevation in egr-1 expression in response to hormone treatment, suggesting that hormones can play a role in phonotaxis response by modulating midbrain neurons that act as an auditory-motor interface.
Sexual selection in the ring-tailed lemur (Lemur catta): female choice, male mating strategies, and male mating success in a female dominant primate
(2006) Parga, Joyce Ann; Overdorff, Deborah J.
Where male-male mating competition is intense, males are frequently larger than females, or have weaponry (e.g. enlarged canines) that females lack. Male dominance over females is often thought to be a by-product of selection for superior size and aggression. Paradoxically, some Malagasy primates show aggressive male-male competition over access to mates, yet lack sexual dimorphism in body size and dentition, and exhibit female dominance over males. This study’s purpose was to investigate female choice and male mating strategies in one such species, the ring-tailed lemur (Lemur catta), to compare the success of physically combative male mating strategies versus alternative non-combative strategies (i.e. sneak copulations). Data were collected across five breeding seasons (2000-2004) on St. Catherines Island, USA, on a provisioned free-ranging L. catta population. Four distinct L. catta groups were studied, two per breeding season, each group having 4-8 females and 2-4 non-natal males. The most commonly used male mating tactics were those that depended on physical contest competition among males. Alpha males often used their dominance status to gain first access to an estrus female, while non-alpha males frequently employed the use of dominance rank reversals as a mating strategy, which required aggressive challenges of more dominant males. Sneak and evasive copulations were also used, though much less often. Male sexual coercion of a female was also documented for the first time in this species. Male inter-troop transfer may be considered a successful mating strategy as well, for females in this study showed greater sexual preference for novel males, and males had higher mating success following a transfer. Female multiple mating was found to be extremely common. Although females mated with multiple males, alpha males were more likely to ejaculate earlier with a female than subordinate males, which may result in alpha males having higher reproductive success. In conclusion, physically combative competition appears to be critical to male mating success in L. catta. These findings provide further support for the hypothesis that sexual monomorphism in this species may have evolved because sperm competition or male stamina is more important than large body size in determining male reproductive success.
Systematics and the evolution of calls and mating preferences on Túngara frogs (genus Engystomops)
(2007) Ron, Santiago R.; Cannatella, David C.
Sexually selected traits are among the most costly, complex, and conspicuous elements of the phenotype. In polygynous reproductive systems, they evolve under strong selection by females. Why females favor those traits, however, is an on-going debate. Here, I use túngara frogs as a model system to study the evolution of communication under sexual selection. The wealth of available information on the behavior, neurophysiology, and reproductive biology of túngara frogs make them an ideal system to understand the patterns of signal evolution and explore the processes that have shaped them. In chapter 1 and 2, I review the taxonomy of túngara frogs (Engystomops) from western Ecuador. I describe three new species including their external morphology and advertisement calls. In chapter 3, I explore the phylogenetic relationships of túngara frogs, testing the support for alternative relationships previously reported for this group. The new phylogeny provides the framework for the comparative analysis carried out in chapters 4 and 5. In chapter 4, I present new female preference and male advertisement call data to test the sensory exploitation hypothesis of sexual selection. Using ancestral character reconstruction, I found that female preferences for complex calls did not originated before the appearance of complex calls, as predicted by sensory exploitation. Instead, my results suggest that the origin of complex calls and their preference originated at similar times. Finally, in chapter 5, I analyze the macroevolutionary patterns of call variation in male túngara frogs. A generalized least squares model demonstrates that advertisement calls have a strong phylogenetic signal. Although most species in Engystomops have distinctive calls, they share a common acoustic structure with two components that evolve at different rates. I did not found evidence of greater call differentiation among sympatric species relative to allopatric species.