Age Estimation using Phalangeal Skeletochronology in Northern Crawfish Frogs, Lithobates areolatus circulosus (Amphibia: Anura: Ranidae), from Arkansas

Abstract

As an obligate crayfish burrow dweller, crawfish frogs have historically occupied a relatively narrow ecological niche throughout their distribution in the tall grass prairies and grasslands of the central and southcentral United States (Redmer 2000; Powell et al. 2016; Lannoo et al. 2018). Habitat loss and shifting climate patterns pose as major threats to the continued existence of this species (Lannoo and Stiles 2017). In Arkansas, the Northern Crawfish Frog, Lithobates areolatus circulosus, occurs in only 19 of its 75 counties (Trauth et al. 2004; Trauth and Holt 2017). Because of their secretive nature, late winter-early spring breeding season, and current protected status by the Arkansas Game and Fish Commission, this species remains a rarity in most museum collections in the state (Trauth et al. 2004). Moreover, only anecdotal information exits regarding any aspect of their natural history in Arkansas (Trauth et al. 1990). In the present study, we chose to conduct a phalangeal skeletochronological investigation of the Northern Crawfish Frog utilizing museum specimens (n = 10) deposited in the herpetological collection (ASUMZ 13900, 14150, 31084-86, 33746-49, 33611) housed in the Arkansas Center for Biodiversity Collections located at Arkansas State University. Four frogs included in this sample were recently collected by SET while road cruising on Turkey Pond Loop (35.2147195N, 92.7567921W) in Conway County on the 20 and 27 February, 2018. Our goals were to estimate the age of individuals within this small Arkansas frog sample by counting annular lines of arrested growth (LAGs) and compare these results with the age estimates found for this frog by Redmer (2000), who utilized the same histological technique on a crawfish frog population in southern Illinois. The distal phalanx (Fig. 1) of the 4 toe of the left hind foot from each frog was removed and placed into either 70% ethanol (historic specimens) or 10% neutral buffered formalin for fresh toes. Then, we treated all toes with a decalcifying solution (1% hydrochloric acid) Figure 1. Photomicrograph of a transverse section through the distal phalanx of Lithobates areolatus circulosus (ASUMZ 33748) revealing phalangeal bone (Pb). Sm = striated muscle.