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opencc-zeroMar 2024View details →

Data and code for: Partitioning variance in a signaling trade-off under sexual selection reveals among-individual covariance in trait allocation

Understanding the evolution of traits subject to trade-offs is challenging because phenotypes can (co)vary at both the among- and within-individual levels. Among-individual covariation indicates consistent, possibly genetic, differences in how individuals resolve the trade-off, while within-individual covariation indicates trait plasticity. There is also the potential for consistent among-individual differences in behavioral plasticity, although this has rarely been investigated. We studied the sources of (co)variance in two characteristics of an acoustic advertisement signal that trade off with one another and are under sexual selection in the gray treefrog, Hyla chrysoscelis: call duration and call rate. We recorded males on multiple nights calling spontaneously and in response to playbacks simulating different competition levels. Call duration, call rate, and their product, call effort, were all repeatable both within and across social contexts. Call duration and call rate covaried negatively, and the largest covariance was at the among-individual level. There was extensive plasticity in calling with changes in social competition, and we found some evidence for among-individual variance in call rate plasticity. The significant negative among-individual covariance in trait values is perpendicular to the primary direction of sexual selection in this species, indicating potential limits on the response to selection.

opencc-zeroSep 2022View details →

Data from: Why are animals conspicuously colored? Evolution of sexual versus warning signals in land vertebrates

Conspicuous colors (e.g. red, yellow, blue) have evolved numerous times across animals. But the function of this coloration can differ radically among species. Many species use this coloration as a sexual signal to conspecifics, whereas others use it as a warning signal to predators. Why do different species evolve conspicuous coloration in association with one function as opposed to the other? We address this question in terrestrial vertebrates (tetrapods) using phylogenetic approaches and test whether day-night activities of species help determine these patterns. Using phylogenetic logistic regression, we found that conspicuous, sexually dimorphic coloration is significantly associated with diurnal lineages (e.g. many birds and lizards). By contrast, the evolution of warning signals was significantly associated with large-scale clades that were ancestrally nocturnal (e.g. snakes, amphibians), regardless of the current diel activity of species. Overall, we show that the evolution of conspicuous coloration as warning signals or sexual signals is influenced by the ecology of species, both recently and in the ancient past.

opencc-zeroOct 2021View details →

Divergent sexual signals reflect costs of local parasites

Many closely related populations are distinguished by variation in sexual signals and this variation is hypothesized to play an important role in reproductive isolation and speciation. Within populations, there is considerable evidence that sexual signals provide information about the incidence and severity of parasite infections, but it remains unclear if variation in parasite communities across space could play a role in initiating or maintaining sexual trait divergence. To test for variation in parasite-associated selection, we compared three barn swallow subspecies with divergent sexual signals. We found that parasite community structure and host tolerance to ecologically similar parasites varied between subspecies. Across subspecies we also found that different parasites were costly in terms of male survival and reproductive success. For each subspecies, the preferred sexual signal(s) were associated with the most costly local parasite(s), indicating that divergent signals are providing relevant information to females about local parasite communities. Across subspecies, the same traits were often associated with different parasites, indicating that parasite-sexual signal links are quite flexible and may evolve relatively quickly. This study provides evidence for 1) variation in parasite communities and 2) different parasite-sexual signal links among three closely related subspecies with divergent sexual signal traits, suggesting that parasites may play an important role in initiating and/or maintaining the divergence of sexual signals among these closely related, yet geographically isolated populations.

Fig. 3 in Sexual Signaling in Periodical Cicadas, Magicicada spp. (Hemiptera: Cicadidae)

Fig. 3. Sonograms of M. septendecim wing flick (A) and synthetic wing flicks produced by a 12 V electric relay (B), a finger snap (C), a piece of paper flicked rapidly (D), and an ordinary electric light switch (E).

Fig. 1 in Sexual Signaling in Periodical Cicadas, Magicicada spp. (Hemiptera: Cicadidae)

Fig. 1. Stylized sonogram of male call/female wing flick courtship duet for M. -decim. The male begins with court I (CI) calls; the female answers each call with a wing flick. After several such interactions, male begins court II (CII) calling. After the male ceases CII calling, the female wing flicks in response, and the male begins court III (C III) calling. Number of call phrases in each stage of the sexual sequence varies. See Table 2 for descriptions of the signals.

Fig. 4 in Sexual Signaling in Periodical Cicadas, Magicicada spp. (Hemiptera: Cicadidae)

Fig. 4. Sonogram of male M. -decim call phrase (A), M. -cassini call phrase (B) and fragment of M. -decula calling song (C) with female wing flick response. Female response (marked with asterisk) is a broad-frequency sound. Wing flick sounds enhanced and extraneous background noise removed for clarity.

Fig. 6 in Sexual Signaling in Periodical Cicadas, Magicicada spp. (Hemiptera: Cicadidae)

Fig. 6. Responses of female M. septendecim to playbacks of artificial, pure tone calls and portions of calls against artificial background choruses of different intensities. Females were scored as responding positively if they produced one or more wing flick signals in response to a playback. Data are presented as proportion of positive responses for specific call and background condition given the total number of trials with those experimental conditions. At all background intensities, whole calls (squares) were more likely to elicit responses than either main portion only (circles) or slur portion only (triangles). At higher background intensities, the effectiveness of whole calls was reduced (Kruskal-Wallis One Way ANOVA z = 420, p ≤ 0.001), as was the effectiveness of main portion only (Kruskal-Wallis One Way ANOVA z = 64, p ≤ 0.001), while the effectiveness of slurs alone was increased (Kruskal-Wallis One Way ANOVA z = 44, p ≤ 0.001).

Fig. 2 in Sexual Signaling in Periodical Cicadas, Magicicada spp. (Hemiptera: Cicadidae)

Fig. 2. Sonogram of male M. -decim call and interference buzz of nearby male, with stylized explanatory sonogram above.

Fig. 5 in Sexual Signaling in Periodical Cicadas, Magicicada spp. (Hemiptera: Cicadidae)

Fig. 5. Timing of female wing flick after end of male call at different ambient air temperatures. 222 individual wing flicks produced by 161 individual females were measured.