Perspectives on the repeated evolution of paraphalanges through the lens of theoretical biology

FONTANARROSA, GABRIELA; FRATANI DA SILVA, JESSICA; VERA MIRIAM CORINA; ABDALA, VIRGINIA; RUSSELL, ANTHONY

Congreso; 1° Congreso Latinoamericano Evolución; 2021

Sociedad chilena de evolución, Asociación colombiana de biología evolutiva, Sociedad argentina de biología evolutiva

Paraphalanges are paired skeletal structures associated with some metacarpo-phalangeal and interphalangeal joints of gekkotan lizards. They represent an extraordinary case of repeated evolution within members of two closely related families of the Gekkota. As these structures exhibit great regularity in their distribution among non-related taxa, it is pertinent to ask whether they rely upon similar developmental mechanisms. In this contribution, we conduct, from the perspective of theoretical biology, a topograpcashical analysis of paraphalangeal distribution encompassing joints within digital rays, and a morphospatial analysis that compares theoretical and empirical models. Our sample consists of 30 cases representing 14 of the 16 genera for which paraphalanges have been described. We reveal a two-dimensional pattern while comparing among distributions. There is a distal to proximal decreasing gradient of paraphalanx occurrence, beginning at the pre-ungual interphalangeal joint. Latero-medially, joint sets can be grouped according to the frequency with which paraphalanges occur; this coincides with sets of joints that are proposed to be established simultaneously during development across the digital array. Both patterns appear to reflect the mechanisms of dactylo- and phalangeo-genesis that have previously been proposed for squamates. Moreover, this pattern might not be a matter of chance, as the observed configurations correspond to a tiny proportion (0.007%) of the theoretical morphospace. This contribution both quantifies the degree of restriction within a theoretical morphospace of the potential distribution of paraphalanges and provides a conceptual linkage to the developmental mechanisms that may assist us in understanding more about the origin of these intriguing structures.