Agkistrodon piscivorus (Lacepede, 1789)

Burbrink, Frank T. & Guiher, Timothy J., 2015, Considering gene flow when using coalescent methods to delimit lineages of North American pitvipers of the genus Agkistrodon, Zoological Journal of the Linnean Society 173 (2), pp. 505-526 : 521-522

AGKISTRODON PISCIVORUS ( LACEPÈDE 1789)

Northern Cottonmouth

Holotype: Unknown.

Type locality: ‘Carolina’ ( Lacépède, 1789), restricted to Charleston, SC, by Schmidt (1953).

Etymology: Specific epithet refers to dietary habit, derived from Latin pisces and vorare, translated as ‘fish’ and ‘to devour’, respectively.

Synonymy: This species comprises the previously recognized subspecies A. p. piscivorus ( Lacépède, 1789) and A. p. leucostoma ( Troost, 1836).

Diagnosis: Combining characteristics for the subspecies Agkistrodon piscivorus piscivorus and Agkistrodon piscivorus leucostoma , we provide a diagnosis for A. piscivorus . The Northern Cottonmouth ( A. piscivorus ) is a medium- to large-bodied semi-aquatic pit viper with an average adult size of 76–114 cm and a maximum size of 188 cm ( Gloyd & Conant, 1990; Conant & Collins, 1991), with a ratio of tail to total length of 0.13–0.19 in males and 0.12–0.18 in females. They possess a single anal plate, keeled dorsal scales and typically 25 midbody scale rows (range 23–27; Gloyd & Conant, 1990). Subcaudals range from 38 to 53 in males and from 42 to 53 in females, whereas ventral scales number 128–142 with no variation between sexes ( Gloyd & Conant, 1990). Supralabials and infralabials range from 6 to 10 (mode 8) and 8 to 12 (mode 11), respectively and total postoculars + suboculars range from 1 to 4 (mode 3; Gloyd & Conant, 1990). A combination of geography and colour pattern distinguishes the Northern Cottonmouth from the Florida Cottonmouth. There are 10–17 dark cross-bands on an olive, brown or black background, whereas A. conanti features 11–16 crossbands. Crossbands in A. piscivorus are often indistinguishable from the ground colour in adults, yet may be prominent or subdued in adult A. conanti . The head is typically black or brown, lacking vertical rostral stripes; a dark cheek stripe is present in juveniles but may be subdued or indistinguishable from the ground colour in adults yet often present in adult A. conanti ( Gloyd & Conant, 1990; Conant & Collins, 1991). The Northern Cottonmouth occupies lower elevations throughout the south-eastern USA from south-eastern Virginia to central Georgia, east of the Appalachian Mountains, north to southern Illinois and eastern Kansas, south into central Texas in the west, whereas the Florida cottonmouth ( A. conanti ) ranges from southern Florida to approximately Savannah Georgia, and west to south-eastern Alabama ( Fig. 5B ). Hybridization with the Florida Cottonmouth occurs in the mid- Atlantic coastal plains in southern North Carolina to the southern coastal plains in south-eastern Louisiana and diagnosis may be difficult for some individuals in this area without additional morphological and molecular data ( Fig. 5B ).

Figures

Figure 5. The distribution of species within the Agkistrodon contortrix complex (A) and Agkistrodon piscivorus complex (B) inferred by Bayesian species delimitation. Putative hybrids zones are identified with cross-hatches. Distributions are adapted from Gloyd & Conant (1990) and the results from ecological niche modelling.