Characterization of Color Pattern Dimorphism in Turks and Caicos Boas, Chilabothrus chrysogaster chrysogaster, on Big Ambergris Cay, Turks and Caicos Islands
Intraspecific color pattern polymorphism (CPP) is widely documented in squamate reptiles and thought to contribute to fitness advantages. Dimorphic striped/spotted CPPs (color pattern dimorphisms [CPDs]) are well characterized among colubrid snakes but are apparently rare among macrostoman lineages. Turks and Caicos Boas (Chilabothrus chrysogaster chrysogaster) are the only booids (superfamily Booidea) known to exhibit a dimorphic striped/spotted CPD within a single population. Based on examination of 737 live wild specimens observed over 12 yr within a population of boas on Big Ambergris Cay, Turks and Caicos Islands, we characterized the striped/spotted CPD and examined potential morphological and spatial correlates of this pattern dimorphism. Contrary to predictions based on studies of similar CPD in colubrid snakes, we found no association between striped or spotted morphs and sex, age, size, or potential morphological correlates. We show that, on average, 15% of the individuals in this population are striped during any given year and that the relative frequency of striped individuals does not appear to change through time, suggesting that the relative frequencies of this polymorphism are stable in this population. Spatial correlation analyses suggested that the striped morph is under-dispersed relative to the spotted morph on Big Ambergris Cay, which might be a product of limited postnatal dispersal or differential habitat preferences. Finally, we described a continuum of color-by-pattern morphs within each pattern class (striped/spotted) in this subspecies which represents a much broader range of color and pattern variation in this species than has been previously recognized.ABSTRACT
Distribution of Chilabothrus c. chrysogaster in the Turks and Caicos Islands. Banks are outlined in light gray, and islands with confirmed records of this species are filled in blue and labeled. Red indicates the location of the study population on Big Ambergris Cay.
Typical spotted (left) and striped (right) morphs of Chilabothrus c. chrysogaster from Big Ambergris Cay, Turks and Caicos Islands. Top photos (A and B) are neonates with orange background color, which is lost as they age. Bottom photos (C and D) are large adult females.
Snout–vent length (SVL) of Chilabothrus c. chrysogaster on Big Ambergris Cay, Turks and Caicos Islands, separated by sex (male/female) and morph (striped/spotted) given as interquartile-range box and whisker plots, where horizontal line represents median, box represents 25th to 75th percentiles, bars represent range, and dots represent outliers. To the right are density plots for each distributed of SVL. Males are in black and females in gray.
Chilabothrus c. chrysogaster morph frequencies by week-long sampling sessions over 12 yr on Big Ambergris Cay, Turks and Caicos Islands. Frequency of striped and spotted CPDs are shown in black and gray, respectively, with the percentage of striped morphs for each sampling session shown above each pair of bars.
Map of Big Ambergris Cay, Turks and Caicos Islands from Google Earth (2017 data) on the top panel. The middle panel shows sampling points for each individual Chilabothrus c. chrysogaster captured on the island, with striped individuals represented by black dots and spotted individuals as gray spots. The bottom panel shows a density map of striped individuals on the island, with blue indicating the lowest densities and pink to yellow colors indicating progressively higher densities.
Examples of mid-dorsal color pattern variation from Chilabothrus c. chrysogaster on Big Ambergris Cay, Turks and Caicos Islands. Note the striped/spotted polymorphism as well as the variation in spotting pattern and color—from almost no spots to double paired dorsal spots and lateral spots and brown vs. gray spots.
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