Evolutionary implications of developmental and functional integration in bat wings

Abstract

This paper addresses how the wing membrane and skeletal system in bats are developmentally and functionally integrated during morphogenesis in the little brown bat (Myotis lucifugus). A truss network is used to quantify changes in the size and shape of the wing membrane during morphogenesis. Growth of the forearm and of third and fifth digits of the manus are also quantified. Principal component analysis indicates that changes in size of the wing (PC-1) contribute 78% of growth variation, whereas shape changes (PC-2, PC-3) contribute only about 18% of growth variation. ANOVA run on component scores shows significant differences in size (PC-1) of the wing between juveniles and sub-adults, whereas no significant difference in shape (PC-2 and 3) of the wing occurs during morphogenesis. In addition, growth compensation is shown to occur among sequentially developing skeletal elements comprising the hand wing. Coefficients of variation were significantly higher for phalangeal lengths than for total wing length and width. Compensation scores generated by summing residual scores produced by bivariate plots of wing bone elements show variable levels of compensation among individuals. However, a plot of scores against wing length shows compensation to occur throughout morphogenesis as scores are not correlated with wing size (r = 0.089). Apparently, selection has favoured a developmental system within which wing shape is conserved while simultaneous plasticity in the hand skeleton helps maintain functional integrity during rapid morphogenesis.