We reassess the coevolution between actinomycete bacteria and fungus-gardening (attine) ants. Actinomycete bacteria are of special interest because they are metabolic mutualists of diverse organisms (e.g., in nitrogen-fixation or antibiotic production) and because Pseudonocardia actinomycetes are thought to serve disease-suppressing functions in attine gardens. Phylogenetic information from culture-dependent and culture-independent microbial surveys reveals (1) close affinities between free-living and ant-associated Pseudonocardia, and (2) essentially no topological correspondence between ant and Pseudonocardia phylogenies, indicating frequent bacterial acquisition from environmental sources. Identity of ant-associated Pseudonocardia and isolates from soil and plants implicates these environments as sources from which attine ants acquire Pseudonocardia. Close relatives of Atta leafcutter ants have abundant Pseudonocardia, but Pseudonocardia in Atta is rare and appears at the level of environmental contamination. In contrast, actinomycete bacteria in the genera Mycobacterium and Microbacterium can be readily isolated from gardens and starter-cultures of Atta. The accumulated phylogenetic evidence is inconsistent with prevailing views of specific coevolution between Pseudonocardia, attine ants, and garden diseases. Because of frequent acquisition, current models of Pseudonocardia-disease coevolution now need to be revised. The effectiveness of Pseudonocardia antibiotics may not derive from advantages in the coevolutionary arms race with specialized garden diseases, as currently believed, but from frequent recruitment of effective microbes from environmental sources. Indeed, the exposed integumental structures that support actinomycete growth on attine ants argue for a morphological design facilitating bacterial recruitment. We review the accumulated evidence that attine ants have undergone modifications in association with actinomycete bacteria, but we find insufficient support for the reverse, modifications of the bacteria resulting from the interaction with attine ants. The defining feature of coevolution—reciprocal modification—therefore remains to be established for the attine ant-actinomycete mutualism.

https://bioone.org/journals/Evolution/volume-62/issue-11/j.1558-5646.2008.00501.x/Coevolution-between-Attine-Ants-and-Actinomycete-Bacteria-A-Reevaluation/10.1111/j.1558-5646.2008.00501.x.pdf

Coevolution between Attine Ants and Actinomycete Bacteria: A Reevaluation

The process of reproductive caste determination in eusocial insect colonies is generally understood to be mediated by environmental, rather than genetic factors. We present data demonstrating unexpected genetic differences between reproductive castes in a variant of the rough harvester ant, Pogonomyrmex rugosus var. fuscatus. Across multiple loci, queens were consistently more homozygous than expected, while workers were more heterozygous. Adult colony queens were divided into two highly divergent genetic groups, indicating the presence of two cryptic species, rather than a single population. The observed genetic differences between castes reflect differential representation of heterospecific and conspecific patrilines in these offspring groups. All workers were hybrids; by contrast, winged queens were nearly all pure-species. The complete lack of pure-species workers indicates a loss of worker potential in pure-species female offspring. Hybrids appear to be bipotential, but do not normally develop into reproductives because they are displaced by pure-species females in the reproductive pool. Genetic differences between reproductive castes are expected to be rare in non-hybridizing populations, but within hybrid zones they may be evolutionarily stable and thus much more likely to occur.

http://www.asu.edu/clas/sirgtools/Proc.Royal%20Soc.%20Biol.,%20Ser.%20B-2002.pdf

Extreme genetic differences between queens and workers in hybridizing Pogonomyrmex harvester ants

Great Basin Naturalist

Gloger's rule is an ecogeographical rule that links animal colouration with climatic variation. This rule is named after C.W.L. Gloger who was one of the first to summarise the associations between climatic variation and animal colouration, noting in particular that birds and mammals seemed more pigmented in tropical regions. The term 'Gloger's rule' was coined by B. Rensch in 1929 and included different patterns of variation from those described by Gloger. Rensch defined the rule in two ways: a simple version stating that endothermic animals are predicted to be darker in warmer and humid areas due to the increased deposition of melanin pigments; and a complex version that includes the differential effects of humidity and temperature on both main types of melanin pigments - eu- and phaeo-melanin. The blackish eu-melanins are predicted to increase with humidity, and decrease only at extreme low temperatures, while the brown-yellowish phaeomelanins prevail in dry and warm regions and decrease rapidly with lower temperatures. A survey of the literature indicates that there is considerable variation/confusion in the way Gloger's rule is understood (based on 271 studies that define the rule). Whereas the complex version is hardly mentioned, only a quarter of the definitions are consistent with the simple version of Gloger's rule (darker where warm and wet), and most definitions mention only the effects of humidity (darker where wet). A smaller subset of studies define the rule based on other correlated climatic and environmental variables such as vegetation, latitude, altitude, solar radiation, etc., and a few even contradict the original definition (darker where cold). Based on the literature survey, I synthesised the qualitative (N = 124 studies) and quantitative (meta-analytically, N = 38 studies, 241 effects) evidence testing the simple version of Gloger's rule (I found no tests of the complex version). Both lines of evidence supported the predicted effects of humidity (and closely linked variables) on colour variation, but not the effects of temperature. Moreover, humidity effects are not restricted to birds and mammals, as the data indicate that these effects also apply to insects. This suggests that the simple version of Gloger's rule as originally defined may not be valid, and possibly that the rule should be re-formulated in terms of humidity effects only. I suggest, however, that more data are needed before such a reformulation, due to potential publication biases. In conclusion, I recommend that authors cite Rensch when referring to Gloger's rule and that they make clear which version they are referring to. Future research should concentrate on rigorously testing the validity and generality of both versions of Gloger's rule and establishing the mechanism(s) responsible for the patterns it describes. Since humidity seems to be the core climatic variable behind Gloger's rule, I suggest that the two most plausible mechanisms are camouflage and protection against parasites/pathogens, the latter possibly through pleiotropic effects on the immune system. Understanding the processes that lead to climatic effects on animal colouration may provide insights into past and future patterns of adaptation to climatic change.

A review of Gloger's rule, an ecogeographical rule of colour: definitions, interpretations and evidence.

We revise and key Trachymyrmex ants occurring in North America north of Mexico. We recognize nine species, including one new species from southern Arizona: T. arizonensis (Wheeler), T. carinatus Mackay & Mackay, T. desertorum (Wheeler), T. jamaicensis (Andre), T. nogalensis Byars, T. pomonae Rabeling & Cover sp. nov., T. septentrionalis (McCook), T. smithi Buren, and T. turrifex (Wheeler). Two infraspecific taxa are synonymized: T. smithi neomexicanus Cole syn. nov. (= T. smithi) and T. turrifex caroli Wheeler syn. nov. (= T. turrifex). We briefly characterize the previously undescribed queens of T. desertorum and T. nogalensis, and the males of T. desertorum and T. turrifex. We include keys for the identification of workers, queens and males, along with distribution maps for all species. A phylogenetic analysis of DNA sequence information for parts of the mitochondrial gene Cytochrome Oxidase I and the first intron of the F1copy of the nuclear protein-coding gene Elongation Factor 1-α is used to characterize the intraversus inter-specific genetic variation of several populations per species. The molecular phylogenetic analysis supports our taxonomic conclusions concerning the North American Trachymyrmex species.

/pdf/a-review-of-the-north-american-species-of-the-fungus-2yevir2f0z.pdf

A review of the North American species of the fungus-gardening ant genus Trachymyrmex (Hymenoptera: Formicidae)

/pdf/ants-of-the-nevada-test-site-4e1mdox8p8.pdf

Ants of the Nevada Test Site.

Descriptions of seven new western ants. (Hymenop.: Formicidae)

/pdf/studies-of-new-mexico-ants-vii-the-genus-pogonomyrmex-with-1f83khc4zs.pdf

Studies of New Mexico ants. VII. The genus Pogonomyrmex with synonymy and a description of a new species (Hymenoptera: Formicidae).

/pdf/a-new-subspecies-of-trachymyrmex-smithi-hymenoptera-tsrr0vnfuf.pdf

A new subspecies of Trachymyrmex smithi (Hymenoptera: Formicidae) from New Mexico.

/pdf/paramyrmica-a-new-north-american-genus-of-ants-allied-to-148gqj264h.pdf

A. C. Cole

Papers

Ants of the Nevada Test Site.

Descriptions of seven new western ants. (Hymenop.: Formicidae)

Studies of New Mexico ants. VII. The genus Pogonomyrmex with synonymy and a description of a new species (Hymenoptera: Formicidae).

A new subspecies of Trachymyrmex smithi (Hymenoptera: Formicidae) from New Mexico.

Paramyrmica, a new North American genus of ants allied to Myrmica Latreille. (Hymenoptera: Formicidae).