No ontogenetic shift in the realised trophic niche but in Batesian mimicry in an ant-eating spider.

In predators an ontogenetic trophic shift includes change from small to large prey of several different taxa. In myrmecophagous predators that are also mimics of ants, the ontogenetic trophic shift should be accompanied by a parallel mimetic change. Our aim was to test whether ant-eating jumping spider, Mexcala elegans, is myrmecomorphic throughout their ontogenetic development, and whether there is an ontogenetic shift in realised trophic niche and their mimetic models. We performed field observations on the association of Mexcala with ant species and investigated the natural prey of the ontogenetic classes by means of molecular methods. Then we measured the mimetic similarity of ontogenetic morphs to putative mimetic models. We found Mexcala is an inaccurate mimic of ants both in the juvenile and adult stages. During ontogenesis it shifts mimetic models. The mimetic similarity was rather superficial, so an average bird predator should distinguish spiders from ants based on colouration. The realised trophic niche was narrow, composed mainly of ants of different species. There was no significant difference in the prey composition between ontogenetic stages. Females were more stenophagous than juveniles. We conclude that Mexcala is an ant-eating specialist that reduces its prey spectrum and shifts ant models during ontogenesis.

The first cytogenetic characterization of atemnids: pseudoscorpions with the highest chromosome numbers (Arachnida: Pseudoscorpiones).

The karyotypes of pseudoscorpions of the family Atemnidae (Arachnida: Pseudoscorpiones) were studied for the first time. Karyotype data for 7 species have been obtained. The diploid chromosome numbers of most species considerably exceed the numbers reported in pseudoscorpions so far, with males ranging between 65 and 143. In spite of this, the sex chromosome system of atemnids is characterized by the same features that are found in the majority of other pseudoscorpions with an X0 system; the X chromosome is metacentric and is the largest chromosome or one of the largest chromosomes of the karyotype. Male meiotic cells of Atemnus politus contain 1 or 2 autosome multivalents; most specimens had 2 multivalents. The multivalents were composed of 4, 6, 8 or 10 chromosomes. Multivalent number and structure was consistent within each of the studied individuals. The same number of chromosomes in all of the males examined suggests that multivalents are generated by reciprocal translocations. The high diversity of multivalents suggests considerable range of translocation heterozygosity in the studied population.