Cryptic speciation in the fungus-growing ants Cyphomyrmex longiscapus Weber and Cyphomyrmex muelleri Schultz and Solomon, new species (Formicidae, Attini)

Abstract

Summary. Nesting in abundance on stream embankments in the wet forests of Panama, the fungus-growing ant Cyphomyrmex longiscapus sensu lato has become a model organism for the study of behavior, ecology, mating frequency, cultivar specificity, pathogenesis, and social parasitism in the attine agricultural symbiosis. Allozyme markers, morphology, and other evidence indicate that C. longiscapus s.l. is in fact a complex of two species, one of which is new to science and described here as Cyphomyrmex muelleri Schultz and Solomon, new species. Although both species occur sympatrically in the same microhabitats and are ecologically, behaviorally, and morphologically quite similar, they consistently cultivate two distantly related fungal symbionts. Thus, each of the two sibling ant species is specialized on a distinct cultivar species, contradicting the conclusions of a previous study. Information is provided for reliably separating the two ant species; morphometrics, ecology, behavior, biogeography, and natural history are summarized. Possible evolutionary mechanisms underlying cryptic speciation in C. longiscapus s.l. are discussed.

Symbiont fidelity and the origin of species in fungus-growing ants

“…2, C. longiscapus and C. muelleri, all occurring 5.3 to 6.9 million years ago. Although this pattern is consistent with a prior hypothesis that shifts in fungal cultivar association may have driven speciation in ants of the C. wheeleri group 31 , it is also consistent with alternative hypotheses, including those in which ant speciation preceded cultivar shifts. It should also be noted that even though the combined nuclear and mitochondrial K2P-corrected distances between C. wheeleri sp.…”

“…longiscapus n. sp. 1 and 2 31 ), currently circumscribed ant species consist of additional, previously undetected, sibling species. C. wheeleri and C. muelleri are each divided into two distinct geographic species, Texas versus California (K2P-corrected distance = 0.11) and Ecuador versus Panama (K2P-corrected distance = 0.06), respectively.…”

“…1), even though nests of the two species occur in sympatry and, indeed, may be separated by only a few centimetres in some localities 12,26,[31][32][33] . Based on evidence from morphology and biogeography, it was previously hypothesized that C. muelleri may be derived from an ancestor resembling C. longiscapus s.l.…”

“…Based on evidence from morphology and biogeography, it was previously hypothesized that C. muelleri may be derived from an ancestor resembling C. longiscapus s.l. and that the origin of C. muelleri may have coincided with, or even have been driven by, a switch from the Clade 1 to Clade 2 cultivar 31 . The younger evolutionary age of Clade 2 relative to Clade 1 16 is consistent with this scenario, as is experimental work demonstrating that Clade 2-cultivating Panamanian C. muelleri ants accept the cultivar of C. longiscapus, whereas C. longiscapus ants do not readily accept the cultivar of C. muelleri 33,34 , reflecting an asymmetric ancestral/derived host-tolerance pattern also known from insect-plant coevolution 35 .…”

Patterns of male parentage in the fungus-growing ants

“…2. C. longiscapus (Mueller and Wcislo 1998) has also been found to consist of two species (Schultz et al 2002), but only the nominal species is included here.…”