Frog Sex! A photo that lead to a publication.

Cruziohyla calcarifer (Splendid leaf-frog) and Agalychnis callidryas (Red-eyed tree frog).  Reproductive behavior.  Cruziohyla calcarifer is a nocturnal canopy tree frog that can be found in primary lowland forests from Honduras to Ecuador.  It is a medium sized frog (males 51 to 81 mm SVL, females 61 to 87 mm) that reproduces in puddles among large fallen trees (Caldwell 1994. Herpetol. Nat. Hist. 2:57-66).  It is an under-studied species because it is nocturnal and favors the canopies, however, habitat destruction, pet trade collecting, and crop spraying are believed to be steadily reducing these primary forest obligates.  Agalychnis callidryas is also a nocturnal tree frog that can be found in lowland and premontane slopes from Mexico to Panama.   Males can reach up to 59 mm SVL and females 77 mm (Savage 2002 The Amphibians and Reptiles of Costa Rica, University of Chicago Press, Chicago, Illinois).  It reproduces in puddles and pools of water with vegetation hanging overtop.  Although it is commonly found in the pet trade, it is known to thrive in secondary forests and areas with some human alteration.

Atypical amplexus has been found repeatedly in anurans, ranging from male-male amplexus (Mollov et al. 2010. Biharean Biologist 4:121-125), interspecific amplexus (Lamb et al. 1990. J. Evol. Biol. 3:295-309), necrogamy (Gomez-Hoyos et al. 2012. Herpetol. Notes 5:497-498), and amplexus with inanimate objects (Streicher 2008. Herpetol. Rev. 39:75).  While less common than interspecific amplexus, intergeneric amplexus has been reported in both tropical and temperate species (Stynoski et al. 2013. Herpetol. Rev. 44:129-130; Grogan and Grogan 2011. Herpetol. Rev.89-90; Manzano and Corzas 2011. Herpetol. Rev. 42:84).  As a means of reproductive interference, intergeneric amplexus has been found to have adverse fitness and evolutionary effects for at least one of the species and can lead to sexual exclusion, spatial, temporal, or habitat segregation, changes in life history parameters, and reproductive character displacement (Gröning and Hochkirch 2008 The Quart. Rev. of Biol. 83:257-282).  Here, we report amplexus between two male individuals from unrelated taxa.

At ~19:00h on 21 April 2013, a male A. callidryas was observed in amplexus with a male C. calcarifer in a private forest in Sarapiqui, Costa Rica (10.43582777°N, -84.044525°W, 35 m elev.)(Fig. 1).  They were sighted about 2.5 m high on a branch. The frogs were found in at the edge of a clearing adjacent to a primary forest that has experienced selective logging within the last 20 years.

D. Blaine Marchant (e-mail: dbmarchant@ufl.edu) University of Florida Biology Department, Gainesville, Florida; Tess Herman and Adam C. Stein Council for International Educational Exchange, Monteverde, Costa Rica.