Female Sensory System Research Articles

Influence of ambient water coloration on habitat and conspecific choice in the female Lake Malawi cichlid, Metriaclima zebra.

Female cichlid fish living in African great lakes are known to have sensory systems that are adapted to ambient light environments. These sensory system adaptations are hypothesized to have influenced the evolution of the diverse male nuptial coloration. In rock-dwelling Lake Malawi mbuna cichlids, however, the extent to which ambient light environments influence female sensory systems and potentially associated male nuptial coloration remains unknown. Yet, the ubiquitous blue flank coloration and UV reflection of male mbuna cichlids suggest the potential impacts of the blue-shifted ambient light environment on these cichlid's visual perception and male nuptial coloration in the shallow water depth in Lake Malawi. In the present study, we explored whether and how the sensory bias of females influences intersexual communication in the mbuna cichlid, Metriaclima zebra. A series of choice experiments in various light environments showed that M. zebra females 1) have a preference for the blue-shifted light environment, 2) prefer to interact with males in blue-shifted light environments, 3) do not show a preference between dominant and subordinate males in full-spectrum, long-wavelength filtered, and short-wavelength filtered light environments, and 4) show a "reversed" preference for subordinate males in the UV-filtered light environment. These results suggest that the visual perception of M. zebra females may be biased to the ambient light spectra in their natural habitat by local adaptation and that this sensory bias may influence the evolution of blue and UV reflective patterns in male nuptial coloration.

A test of sensory exploitation in the swordtail characin (Corynopoma riisei) based on colour matching between female prey and a male ornament

The sensory exploitation hypothesis states that pre-existing biases in female sensory systems may generate strong selection on male signals to match such biases. As environmental conditions differ between populations, sexual preferences resulting from natural selection are expected to vary as well. The swordtail characin (Corynopoma riisei) is a species in which males carry a flag-like ornament growing from the operculum that has been proposed to function as a prey mimic to attract females. Here, we investigated if female plasticity in feeding preferences is associated with plasticity in preference for an artificial male ornament in this species. Females were trained for 10 days by offering them differently coloured food items and were then tested for changes in preferences for differently coloured artificial male ornaments according to foraging experience. We found a rapid and pronounced change in female preference for the colouration of the artificial ornament according to food training. Thus our results support the possibility that sensory exploitation may act as a driving force for female preferences for male ornaments in this species.

Looking for sexual selection in the female brain

Female mate choice behaviour has significant evolutionary consequences, yet its mechanistic origins are not fully understood. Recent studies of female sensory systems have made great strides in identifying internal mechanisms governing female preferences. Only recently, however, have we begun to identify the dynamic genomic response associated with mate choice behaviour. Poeciliids provide a powerful comparative system to examine genomic responses governing mate choice and female preference behaviour, given the great range of mating systems: from female mate choice taxa with ornamental courting males to species lacking male ornamentation and exhibiting only male coercion. Furthermore, they exhibit laboratory-tractable preference responses without sexual contact that are decoupled from reproductive state, allowing investigators to isolate mechanisms in the brain without physiological confounds. Early investigations with poeciliid species (Xiphophorus nigrensis and Gambusia affinis) have identified putative candidate genes associated with female preference response and highlight a possible genomic pathway underlying female social interactions with males linked functionally with synaptic plasticity and learning processes. This network is positively correlated with female preference behaviour in the female mate choice species, but appears inhibited in the male coercive species. This behavioural genomics approach provides opportunity to elucidate the fundamental building blocks, and evolutionary dynamics, of sexual selection.

Variable courtship song traits in the field cricket Gryllus assimilis fit the features of the female sensory system

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It is a matter of taste: chemical signals mediate nuptial gift acceptance in a neotropical spider

Nuptial gift offering is a courtship trait found among several insect orders and some spider families. Recent studies indicate that this gift-giving behavior in spiders represents the male mating effort acting on female receptivity through a mechanism of foraging motivation. However, little attention has been given to the sensory channels that are influencing female acceptance. To understand the role of these sensory channels in female perception of a nuptial gift, we focused on the nuptial gift of the neotropical spider Paratrechalea ornata (Araneae, Trechaleidae). The nuptial gift of this species is composed of a prey item wrapped in silk, and previous works suggest that visual and/or chemical cues may be involved in inducing female grasping behavior. We isolated sensory channels using mimetic nuptial gifts (artificial items) or by manipulating real nuptial gifts. Isolated visual signals were not responsible for female acceptance, whereas chemical signals found within the nuptial gift silk layer induced female acceptance. Our findings clearly indicate that a chemical signal located in the silk of the nuptial gift is the main attractant channel, and we formulated 2 hypotheses to explain the mechanisms of action in the female sensory system. We also discuss the consequences of such signaling over female acceptance.

Does the environmental context of a signalling male influence his attractiveness?

How sexually selected male signals and female sensory systems have evolved so that females can continue to detect and discriminate between potential mates in the face of environmental noise and changes in signaller density has been well studied for acoustic signals. Far less is known about visual signals. We examined the influence of the local signalling environment on male signal attractiveness in the fiddler crab Uca mjoebergi. We used custom-built robotic crabs in two-stimulus mate choice experiments. Females were presented with two identical signals produced in two different signalling environments (simple and complex). The conspicuousness/attractiveness of male claw waving was unaffected by the local environment (physical or social). Male U. mjoebergi appear to produce a signal that is highly conspicuous across a wide range of naturally occurring signalling environments and females seem to have a sensory system that is capable of coping with high levels of environmental noise.

SEXUAL TENSION: DOES CONFLICT LEAD TO COSTLY MATE CHOICE?1

SEXUAL TENSION: DOES CONFLICT LEAD TO COSTLY MATE CHOICE?1

Sensory Bias as an Explanation for the Evolution of Mate Preferences

The sensory bias model of sexual selection posits that female mating preferences are by-products of natural selection on sensory systems. Although sensory bias was proposed 20 years ago, its critical assumptions remain untested. This paradox arises because sensory bias has been used to explain two different phenomena. First, it has been used as a hypothesis about signal design, that is, that males evolve traits that stimulate female sensory systems. Second, sensory bias has been used as a hypothesis for the evolution of female preference itself, that is, to explain why females exhibit particular preferences. We focus on this second facet. First, we clarify the unique features of sensory bias relative to the alternative models by considering each in the same quantitative genetic framework. The key assumptions of sensory bias are that natural selection is the predominant evolutionary mechanism that affects preference and that sexual selection on preferences is quantitatively negligible. We describe four studies that would test these assumptions and review what we can and cannot infer about sensory bias from existing studies. We suggest that the importance of sensory bias as an explanation for the evolution of female preferences remains to be determined.

Escalation, Retreat, and Female Indifference as Alternative Outcomes of Sexually Antagonistic Coevolution

Verbal and quantitative genetic models of sexually antagonistic coevolution suggest that coevolutionary arms races should be common. Sexual selection favors exaggeration of male persistence traits that are costly to females, and females, in turn, are selected to resist these traits. The heightened resistance by females is thought to then favor further exaggeration in the male trait, leading to an escalating coevolutionary arms race between persistence and resistance traits. Much of this theory, however, is based on an (implicit) assumption that there are tight constraints on how female resistance can evolve. We develop a theory that identifies and relaxes these constraints, allowing female resistance to evolve in a fashion that better reflects known empirical patterns in the evolution of female preference functions (the resistance trait). Our results suggest that evolutionary arms races that lead to the exaggeration of persistence and resistance will be much less common than formerly predicted. Females sometimes evolve indifference to male traits rather than resistance and can even evolve to discriminate against these traits. These alternative outcomes depend on the existence of genetic variance in the components of the female sensory system underlying female resistance and on the strength of natural selection acting on these components. Female indifference tends to evolve when natural selection on the sensory system is weak, and under these conditions, sexually antagonistic coevolution tends not to reduce female fitness significantly at equilibrium. When natural selection on the female sensory system is strong, however, then arms races are more likely, and female fitness is then sometimes significantly depressed at equilibrium. Sexually antagonistic coevolution is thus likely to have strong deleterious effects on population fitness only when female sensory traits are under strong natural selection to perform functions in addition to those involved with mating. Together, these results suggest that identifying the nature of genetic variation in and the strength of natural selection on female resistance should be a central goal of future studies of sexual conflict.

Escalation, Retreat, and Female Indifference as Alternative Outcomes of Sexually Antagonistic Coevolution

Verbal and quantitative genetic models of sexually antagonistic coevolution suggest that coevolutionary arms races should be common. Sexual selection favors exaggeration of male persistence traits that are costly to females, and females, in turn, are selected to resist these traits. The heightened resistance by females is thought to then favor further exaggeration in the male trait, leading to an escalating coevolutionary arms race between persistence and resistance traits. Much of this theory, however, is based on an (implicit) assumption that there are tight constraints on how female resistance can evolve. We develop a theory that identifies and relaxes these constraints, allowing female resistance to evolve in a fashion that better reflects known empirical patterns in the evolution of female preference functions (the resistance trait). Our results suggest that evolutionary arms races that lead to the exaggeration of persistence and resistance will be much less common than formerly predicted. Females sometimes evolve indifference to male traits rather than resistance and can even evolve to discriminate against these traits. These alternative outcomes depend on the existence of genetic variance in the components of the female sensory system underlying female resistance and on the strength of natural selection acting on these components. Female indifference tends to evolve when natural selection on the sensory system is weak, and under these conditions, sexually antagonistic coevolution tends not to reduce female fitness significantly at equilibrium. When natural selection on the female sensory system is strong, however, then arms races are more likely, and female fitness is then sometimes significantly depressed at equilibrium. Sexually antagonistic coevolution is thus likely to have strong deleterious effects on population fitness only when female sensory traits are under strong natural selection to perform functions in addition to those involved with mating. Together, these results suggest that identifying the nature of genetic variation in and the strength of natural selection on female resistance should be a central goal of future studies of sexual conflict.

Male copulatory sensory stimulation induces female ejection of rival sperm in a damselfly

Male damselflies possess very specialized genitalia. Females mate multiply and store sperm in two sperm storage organs, the bursa copulatrix and the spermatheca. During copulation, males physically remove the sperm stored in these organs using their genitalia. I document a novel mechanism by which males gain access to the spermatheca in Calopteryx haemorrhoidalis asturica . The mechanism is based on male stimulation of the female sensory system that controls egg fertilization and laying. During copulation, the aedeagus (a male genitalic structure indirectly involved in sperm transfer) distorts the cuticular plates in the female genital tract that bear mechanoreceptive sensilla. This stimulation results in sperm ejection from the spermatheca. Aedeagus width is positively correlated with the amount of sperm ejected. I propose that males have exploited a pre–existing female sensory bias to gain access to otherwise physically unreachable sperm. These results shed light on the issue of the origin of female preferences in current models of sexual selection and on the evolution of genitalia via sexual selection. It is postulated that females might use this process as a form of post–copulatory sexual selection on the basis of males9 genitalia.

A test of sensory bias for long tails in the house finch

The sensory bias model of sexual selection proposes that female preferences for certain male traits result from biases in the female sensory system that existed prior to the evolution of the preferred trait. Phylogenetic tests of the sensory bias hypothesis have provided evidence for pre-existing bias in several species, but the hypothesis has not been tested relative to elongated tail feathers, a widespread sexually selected trait in birds. Elongated tails occur sporadically across avian taxa, including cardueline finches (family Fringillidae), suggesting that long tails evolved independently in many lineages. To determine whether a female preference for longer tails predated the evolution of long tails in cardueline finches, we tested female preferences for artificially lengthened tail feathers in male house finches,Carpodacus mexicanus. The house finch is a cardueline finch species with a tail that does not appear to be elongated or sexually selected. In mate choice experiments, females did not demonstrate a preference for lengthened tails over controls. This negative result fails to support the hypothesis that elongation of tail feathers resulted from exploitation of a widespread sensory bias.