Can Reproductive Allometry Assess Population Marginality in Crocodilians? A Comparative Analysis of Gulf Coast American Alligator (Alligator mississippiensis) Populations
This study uses the American Alligator (Alligator mississippiensis) to assess the use of reproductive allometry as a tool to infer crocodilian population marginality based on conformation to advantageous life-history strategies. It is hypothesized that reproductive allometry, a morphometric relationship between mother's size and her reproductive output, varies intraspecifically between populations and that this variation reflects population marginality based on size, stress, temporal exploitation, habitat fragmentation, and/or the presence of social hierarchy. This hypothesis is tested using relative comparisons of allometric correlation between a marginal population inundated with saline storm surge from Hurricane Ike in southeastern Texas and a hypothesized unstressed core population in southeastern Louisiana. Heterophil to lymphocyte ratios fail to falsify the hypothesis of a saline stressor. The number of significant morphometric correlations between various parameters, degree of correlation (R2), and slope of correlation between mother and her respective nest and clutch varied greatly between study sites. Reproductive allometry, as a measure of relative population marginality, may provide a cost effective way to prioritize management with local support for crocodilian taxa.
(A) Google Earth satellite image showing relative location of study sites highlighted in white boxes along the Gulf Coast. J. D. Murphree WMA to the left (west) and Las Conchas Marsh to the right (east). (B) Google Earth satellite image of J. D. Murphree WMA relative to Port Arthur, TX. (C) Google Earth satellite image of Las Conchas Marsh east of Slidell, LA.
Pearson correlation matrix indicating strong correlation between maternal morphometrics: adult snout–vent length (AdultSVL), adult body mass (AdultBM), and adult total length (AdultTL). Strong relationships indicate that one morphometric is informative for all other morphometrics in further analyses.
Pearson correlation matrix indicating strong correlation between egg width and egg length, nest diameter and nest height, and clutch mass and egg width. Egg mass, egg length, clutch mass, and nest diameter were used as representative variables in subsequent analyses.
Log-transformed comparison of allometric correlations between a stressed and unstressed population of Alligator mississippiensis. (A) Relationship between egg mass and maternal snout–vent length (SVL) in stressed (gray) and unstressed (black) populations. (B) Egg length vs. SVL. (C) Clutch mass vs. SVL. (D) Nest diameter vs. SVL.
(A) RELATE analysis assessing the level of correlation between mother and nest/clutch morphometrics from Las Conchas Marsh using 999 permutations and Euclidean distance resemblance matrices (Rho = 0.507, significance level = 0.5%). (B) RELATE analysis assessing the level of correlation between mother and nest/clutch morphometrics from J. D. Murphree WMA using 999 permutations and Euclidean distance resemblance matrices (Rho = −0.145, significance level = 69.9%).
Contributor Notes
Associate Editor: B. Stuart.