The leaf beetle Chelymorpha alternans propagates a plant pathogen in exchange for pupal protection.

Many insects rely on microbial protection in the early stages of their development. However, in contrast to symbiont-mediated defense of eggs and young instars, the role of microbes in safeguarding pupae remains relatively unexplored, despite the susceptibility of the immobile stage to antagonistic challenges. Here, we outline the importance of symbiosis in ensuring pupal protection by describing a mutualistic partnership between the ascomycete Fusarium oxysporum and Chelymorpha alternans, a leaf beetle. The symbiont rapidly proliferates at the onset of pupation, extensively and conspicuously coating C. alternans during metamorphosis. The fungus confers defense against predation as symbiont elimination results in reduced pupal survivorship. In exchange, eclosing beetles vector F. oxysporum to their host plants, resulting in a systemic infection. By causing wilt disease, the fungus retained its phytopathogenic capacity in light of its symbiosis with C. alternans. Despite possessing a relatively reduced genome, F. oxysporum encodes metabolic pathways that reflect its dual lifestyle as a plant pathogen and a defensive insect symbiont. These include virulence factors underlying plant colonization, along with mycotoxins that may contribute to the defensive biochemistry of the insect host. Collectively, our findings shed light on a mutualism predicated on pupal protection of an herbivorous beetle in exchange for symbiont dissemination and propagation.

Inheritance, distribution and genetic differentiation of a color polymorphism in Panamanian populations of the tortoise beetle, Chelymorpha alternans (Coleoptera: Chrysomelidae).

Intraspecific variation maintained in natural populations has long intrigued scientists and naturalists. One form of this variation, color polymorphisms, provide a rich opportunity to connect genotypic and phenotypic diversity within an ecological and evolutionary context. The existence of color polymorphisms in Panamanian populations of the Neotropical tortoise beetle, Chelymorpha alternans, has been suspected but never systematically explored. To characterize geographic distribution and underlying genetics we sampled a total of 3819 beetles from 28 sites across Panama, quantifying five distinct phenotypes. Two phenotypes, the "metallic" and "rufipennis" are the most widely distributed phenotypes, occurring in nearly all collecting sites. The "veraguensis" phenotype was found to be restricted to the Western end of the Isthmus and the "militaris" phenotypes restricted to sites east of the canal. Controlled matings between phenotypes and reared offspring revealed no indications of reproductive barriers, even among phenotypes which do not co-occur in nature. Color pattern phenotype is largely controlled by Mendelian assortment of four alleles competing at a single locus. A clear dominance hierarchy exists among alleles, with two being co-dominant. Genomic scans from 32 individuals revealed low levels of genetic differentiation, with a small fraction of the genome showing a high degree of divergence. The easily observed variation among populations, simple genetic architecture, and rearing capabilities, make this a promising system for investigating proximate and ultimate factors of phenotypic variation.

ONE SIZE FITS ALL? RELATIONSHIPS BETWEEN THE SIZE AND DEGREE OF VARIATION IN GENITALIA AND OTHER BODY PARTS IN TWENTY SPECIES OF INSECTS AND SPIDERS.

Hypotheses regarding the function of elaborate male genitalia were tested in a sample of insects and spiders by comparing their allometric values (slopes in log-log regressions on indicators of body size) with those of other body parts. Male genitalia consistently had lower slopes than other body parts. Perhaps as a consequence of this pattern, genitalic size also tended, though less consistently, to have lower coefficients of variation than did the size of other body parts. The morphological details of coupling between males and females in several species clearly indicated that selection favoring mechanical fit is not responsible for these trends. Sexual selection on male courtship structures that are brought into contact with females in precise ways may favor relatively low allometric values, in contrast to the high values seen in the other sexually selected characters (usually visual display devices) that have been studied previously, because a female's own size will influence her perception of the contact courtship devices of a male.