Morphometric analysis of the broad-snouted caiman (Caiman latirostris): An assessment of individuals' clutch, body size, sex, age, and area of origin

Three consecutive questions are tested in the current morphometric study of the broad-snouted caiman (Caiman latirostris): Is there a significant morphometric variation related to clutch-effect, body size, sex, age, area of origin, and environment? Can the group to which a specific individual belongs be predicted? And last, if it is possible to efficiently predict an individual's group using all morphometric variables recorded, is it possible to reduce the number of variables without significantly losing efficiency? Cranial and body morphometric variables were recorded from captive and wild animals. MANOVA, linear discriminant analysis with cross-validation, PCA, and best subset regressions are used in order to answer the questions above. Exploratory studies of relative growth and allometry of reproduction were used to develop models of age estimation, sexual dimorphism, and clutch discrimination.; Log-transformation of data significantly improved sexual dimorphism perception through the reduction of the scaling effect among variables. Except for body-mass, log-transformation did not significantly improve data analysis in relative growth studies. Ratios between variables were consistently less efficient at detecting differences between groups than direct measurements. Multivariate morphometric models are consistently more efficient than univariate growth curves for determining age of animals. Sexual dimorphism in cranial morphometry of broad-snouted caiman can be detected even in young individuals. However, it is frequently impossible to isolate gender from other sources of variation, such as clutch, age, body size, area of origin, and environment. There is a positive correlation between female body size and egg size, hatchlings' body size, and clutch mass. There is a significant negative correlation between female body size and the relative clutch mass (clutch mass/female body mass). Clutch discrimination based on clutch effect and female-family effect (matrilineal lineage) can be used to establish parentage among individuals in small wild populations and captive breeding programs. There is a significant cranial morphometric variation among animals from different study sites. This may be related to some level of reproductive isolation, which may be related to habitat fragmentation. Captive animals present relatively broader snout, cranium, mandible, and external nares; and relatively longer mandibular symphisis than wild individuals.