Mite load predicts the quality of sexual color and locomotor performance in a sexually dichromatic lizard

Abstract

Since Darwin, the maintenance of bright sexual colors has recurrently been linked to mate preference. However, the mechanisms underpinning such preferences for bright colors would not be resolved for another century. Likely, the idea of selection for colors that could decrease the chances of survival (e.g., flashy colors that can inadvertently attract predators) was perceived as counterintuitive. It is now widely accepted that these extreme colors often communicate to mates the ability to survive despite a "handicap" and act as honest signals of individual quality when they are correlated with the quality of other traits that are directly linked to individual fitness. Sexual colors in males are frequently perceived as indicators of infection resistance, in particular. Still, there remains considerable discord among studies attempting to parse the relationships between the variables associating sexual color and infection resistance, such as habitat type and body size. This discord may arise from complex interactions between these variables. Here, we ask if sexual color in male Florida scrub lizards (Sceloporus woodi) is an honest signal of resistance to chigger mite infection. To this end, we use linear modeling to explore relationships between mite load, different components of sexual color, ecological performance, body size, and habitat type. Our data show that that the brightness of sexual color in scrub lizards is negatively associated with the interaction between mite load and body size, and scrub lizards suffer decreased endurance capacity with increases in mite load. Our data also indicate that mite load, performance, and sexual color in male scrub lizards can vary between habitat types. Collectively, these results suggest that sexual color in scrub lizards is an honest indicator of individual quality and further underscore the importance of considering multiple factors when testing hypotheses related to the maintenance of sexual color.

Keywords: honest signals; parasite‐mediated selection; selection for handicap; sexual dichromatism.

Figure 1

(a) Photograph of ventral side of male Florida scrub lizard taken in the field. Note the accumulation of chigger mites in the gular fold (outlined by white square). (b) Magnified image of larval Eutrombicula cinnabaris (chigger mite) sampled from a male scub lizard and slide‐mounted in Hoyer's medium. (c–d) Histograms of the blue color badge and black border of male scrub lizards with median brightness values collected from Florida scrub (FSC) (c) and longleaf pine (LLP) (d). In each histogram, colors have been binned into 10 values and the length of each color segment represents the proportion of each color. (e–f) Chromaticity diagrams of the blue badge color sampled for lizards with median brightness values from FSC and LLP, respectively. Note that chromaticity diagrams are shown as red‐green‐blue (RGB) values with percent blue on the Y‐axis, percent red on the X‐axis, and percent green on the Z‐axis

Figure 2

(a) Box plot showing mite load (range, quantile, and median) for longleaf pine (LLP) and Florida scrub (FSC) habitat types. Median mite load harbored by male scrub lizards is higher in FSC (F _(1,38) = 31.76, p = .001). (b) Mosaic plot showing the proportion of substrate types for which male scrub lizards were initially encountered for LLP and FSC habitat types. The substrate type upon which scrub lizards were encountered is contingent on habitat type (odds ratio = 6.52, p = .001)

Figure 3

(a) Grouped box plot showing male Florida scrub lizard badge color brightness and black border brightness (range, quantile, and median) for longleaf pine (LLP) and Florida scrub (FSC) habitat types. Badge color and black border groups are colored according to the legend. Scrub lizard badge color is darker in LLP (F _(1,38) = 12.32, p = .001) although black border brightness of scrub lizards does not significantly vary between habitat types (F _(1,38) = 0.17, p = .675. (b) Box plot showing scrub lizard endurance (range, quantile, and median) for LLP and FSC habitat types. Scrub lizards collected from LLP have greater endurance (F _(1,38) = 6.57, p = .014), although sprint speed does not significantly vary between habitat types (F _(1,38) = 0.155, p = .659)

Figure 4

Three‐dimensional plot showing the relationships between mass (X‐axis), mite load (Y‐axis), and badge color brightness (Z‐axis) in male Florida scrub lizards. Individual points are denoted in the predicted badge color and are predicted by mass and mite load, where the brightness of scrub lizard badge color increases as mass and mite load increase (p = .014, R ² = .25). In particular, smaller scrub lizards with fewer mites tend to have the darkest colors and larger lizards with more mites have brighter colors that approach gray

Figure 5

Scatter plot showing the predicted negative relationship between mite load and scrub lizard endurance (p = .026, R ² = .24). Scrub lizards with increased mite loads have less endurance than scrub lizards with fewer mites. The gray cloud surrounding the line of best fit is (±) 1 SE

Figure 6

Scatter plot showing the positive relationship between mite load and scrub lizard internal body temperature (Pearson's coefficient = 0.36, p = .017). In captivity, scrub lizards with increased mite loads tend to have higher internal body temperatures than scrub lizards with fewer mites. The gray cloud surrounding the line of best fit is (±) 1 SE