ANTIPREDATOR BLOOD-SQUIRTING AND SEED-HARVESTING ANTS (POGONOMYRMEX) IN THE EVOLUTION OF MYMECOPHAGY IN HORNED LIZARDS (PHRYNOSOMA).

Recent studies on Phrynosoma lizards and their prey have shown a strong dietary connection to well defended harvester ants of the genus Pogonomyrmex having peptide neurotoxin stings evolved specifically as painful defenses against vertebrates. During digestion of these ants a compound(s) from their toxin enters horned-lizard blood becoming a circulating antipredator deterrent. That relationship is explored summarizing new and published occurrences of a resulting blood-squirting defense throughout 17 species, including four clades, and their known dietary inclusion of Pogonomyrmex ants. Data on blood-squirting has been determined during field human capture, staged dog trials, and native canid or felid trials. The horned lizard blood-squirting defense is nearly universal throughout the genus. Eating Pogonomyrmex ants is widespread but poorly studied and not encountered by all populations. Examining the evolution of Phrynosoma myrmecophagy of this specific ant genus greatly broadens our knowledge of the intricate complexities of horned lizards as a unique lineage of myrmecophagy in lizards. Two stages for the evolution of this relationship are envisioned. The blending of plesiomorphic squamate features and apomorphic generic features in this difficult evolutionary coupling of two genera illustrates the complexities of this myrmecophagy dietary specialization of Phrynosoma. This specialized dietary lineage of myrmecophagy in the family Phrynosomatidae enhanced the geographical, elevational, and ecological expansion and diverse evolution of Phrynosoma during their exploitation of a North American keystone genus of ants. [ABSTRACT FROM AUTHOR]