Testes degeneration in ants: a histological study of Gnamptogenys bicolor

Allard, D., Ito, F., Aikawa, Y., Gotoh, A. and Billen, J. 2010. Testes degeneration in ants: a histological study of Gnamptogenys bicolor. —Acta Zoologica (Stockholm) 92 : 372–376. Sperm synthesis in the males of social Hymenoptera is not continuous, as the testes degenerate before the males become sexually active. This article presents the first histological study focusing on the degeneration of testes tissue, using adult males of the ant Gnamptogenys bicolor. At eclosion, spermatogenesis is still in process in the apical part of the testes, while the basal spermatocysts are all packed with mature sperm. During the second week after eclosion, the first signs of degeneration appear as small clear vacuoles inside the spermatocysts, interspersed between maturing sperm cells. Sperm starts migrating into the vasa deferentia shortly after. As spermatocysts void their contents into the vasa deferentia, the follicles start shrinking and losing their shape and the fibrillar capsule tissue gets looser. Cellular breakdown yields dark vacuoles of various density and large granular, multi‐layered bodies.     

Arthropod biodiversity loss and the transformation of a tropical agro-ecosystem

The coffee (Coffea arabica) agro-ecosystem in the Central Valley of Costa Rica was formerly characterized by a high vegetational diversity. This complex system has been undergoing a major transformation to capital-intensive monocultural plantations where all shade trees are eliminated. In this study we examined the pattern of arthropod biodiversity loss associated with this transformation. Canopy arthropods were sampled in three coffee farms: a traditional plantation with many species of shade trees, a moderately shaded plantation with only Erythrina poeppigeana and coffee, and a coffee monoculture. An insecticidal fogging technique was used to sample both canopy and coffee arthropods. Data are presented on three major taxonomic groups: Coleoptera, non-formicid Hymenoptera, and Formicidae. Data demonstrate that the transformation of the coffee agro-ecosystem results in a significant loss of biological diversity of both canopy arthropods as well as arthropods living in coffee bushes. Percentage of species overlap was very small for all comparisons. Furthermore, species' richness on a per tree basis was found to be within the same order of magnitude as that reported for trees in tropical forests. If results presented here are generalizable, this means that conservation efforts to preserve biological diversity should also include traditional agro-ecosystems as conservation units.     

Evidence that gestation duration and lactation duration are coupled traits in primates

Gestation duration and lactation duration are usually treated as independently evolving traits in primates, but the metabolic theory of ecology (MTE) suggests both durations should be determined by metabolic rate. We used phylogenetic generalized least-squares linear regression to test these different perspectives. We found that the allometries of the durations are divergent from each other and different from the scaling exponent predicted by the MTE (0.25). Gestation duration increases much more slowly (0.06 < m < 0.12), and lactation duration much more quickly (0.36 < m < 0.52) with body mass than the MTE predicts. By contrast, we found that the combined duration of gestation and lactation is consistent with the MTE''s predictions (0.22 < m < 0.35). These results suggest that gestation duration and lactation duration might best be viewed as distinct but coupled adaptations. When transferring energy to their offspring, primate mothers must meet metabolically dictated physiological requirements while optimizing the timing of the switch from gestation to lactation in relation to some as-yet-unidentified body-size-related factor.     

Changes in body temperature influence the scaling of VO2max and aerobic scope in mammals

Debate on the mechanism(s) responsible for the scaling of metabolic rate with body size in mammals has focused on why the maximum metabolic rate (VO2max ) appears to scale more steeply with body size than the basal metabolic rate (BMR). Consequently, metabolic scope, defined as VO2max/BMR, systematically increases with body size. These observations have led some to suggest that VO2max, and BMR are controlled by fundamentally different processes, and to discount the generality of models that predict a single power-law scaling exponent for the size dependence of the metabolic rate. We present a model that predicts a steeper size dependence for VO2max than BMR based on the observation that changes in muscle temperature from rest to maximal activity are greater in larger mammals. Empirical data support the model's prediction. This model thus provides a potential theoretical and mechanistic link between BMR and VO2 max.     

Rareness of certain Mediterranean ant species: fact or artifact?

Summary A checklist of the ants recorded during five years in a small urban area (400 m²) in Sant Cugat (Barcelona, Spain) is presented. 23 species nest in the area, 7 species (hypogaeic or parasitic) probably nest and 5 species nest in the vicinity; five additional species have also been recovered from the area. The rarity of some of these (Leptanilla sp.,Hypoponera abeillei (Emery),Cryptopone ochraceum (Mayr),Smithistruma tenuipilis (Emery),Epitritus argiolus Emery,Trichoscapa membranifera Emery,Chalepoxenus muellerianus (Finzi),Anergates atratulus (Schenck),Plagiolepis xene (Schenck),Lasius carniolicus Mayr) and the high number of species suggest that a) rarity in Mediterranean ant species may be explained by the insufficient sampling in time of adequate microhabitats (hypogaeic species) or by the inconspicuousness of social parasitic species, and b) that previously published species lists of ants from Mediterranean habitats might be rather incomplete.     

Ants of the tribe Formicini (Hymenoptera,Formicidae) from Late Eocene amber of Europe

The tribe Formicini (Formicinae) from the Late Eocene Baltic, Bitterfeld, Rovno, and Scandinavian ambers is revised. Ants are recorded for the first time from the Bitterfeld and Scandinavian ambers. Two new genera (Cataglyphoides gen. nov. and Conoformica gen. nov.) and six new species (Cataglyphoides intermedius sp. nov., Conoformica bitterfeldiana sp. nov., Formica kutscheri sp. nov., F. palaeopolonica sp. nov., F. radchenkoi sp. nov., F. zherikhini sp. nov.) are described. A new combination, Cataglyphoides constrictus (Mayr, 1868), comb. nov., is established. A lectotype of Camponotus constrictus Mayr, 1868 and a neotype of Formica phaethusa Wheeler, 1915 are designated. Formica clymene Wheeler, 1915 is recognized as a new synonym of F. phaethusa Wheeler, 1915. An identification key for workers of Formicini species from Late Eocene European ambers is provided.     

The role of an attractive brood pheromone in the obligatory,slavemaking ant,Polyergus breviceps (hymenoptera: Formicidae)

Freeliving workers of Formica occulta, an ant species enslaved by the obligatory slavemaking ant Polyergus breviceps, retrieve and nurse Polyergus pupaejust as well as conspecific pupae in a choice test. No such attraction was found toward pupae of the facultative slavemaker; Formica wheeleri,which also enslaves F. occulta. Formica neogagates,a sympatric species which is not parasitized by either slavemaker, preferentially retrieves and tends conspecific brood over that of Polyergusand F. wheeleri.It is proposed that brood of obligatory slavemaking species must possess an attractive pheromone for slavemaker colony foundation to be successful, since slavemaker brood must be nursed by adult slave workers with no prior exposure to slavemaker brood. An attractive pheromone is not necessary in the brood of facultative slavemakers, since this brood is cared for by newly eclosed slave workers who imprint on the slavemaker brood.     

Allometric scaling of intraspecific space use

Allometric scaling relationships enable exploration of animal space-use patterns, yet interspecific studies cannot address many of the underlying mechanisms. We present the first intraspecific study of home range (HR) allometry relative to energetic requirements over several orders of magnitude of body mass, using as a model the predatory fish, pike Esox lucius. Analogous with interspecific studies, we show that space use increases more rapidly with mass (exponent = 1.08) than metabolic scaling theories predict. Our results support a theory that suggests increasing HR overlap with body mass explains many of these differences in allometric scaling of HR size. We conclude that, on a population scale, HR size and energetic requirement scale allometrically, but with different exponents.     

The evolution of superstitious and superstition-like behaviour

Superstitious behaviours, which arise through the incorrect assignment of cause and effect, receive considerable attention in psychology and popular culture. Perhaps owing to their seeming irrationality, however, they receive little attention in evolutionary biology. Here we develop a simple model to define the condition under which natural selection will favour assigning causality between two events. This leads to an intuitive inequality--akin to an amalgam of Hamilton's rule and Pascal's wager--that shows that natural selection can favour strategies that lead to frequent errors in assessment as long as the occasional correct response carries a large fitness benefit. It follows that incorrect responses are the most common when the probability that two events are really associated is low to moderate: very strong associations are rarely incorrect, while natural selection will rarely favour making very weak associations. Extending the model to include multiple events identifies conditions under which natural selection can favour associating events that are never causally related. Specifically, limitations on assigning causal probabilities to pairs of events can favour strategies that lump non-causal associations with causal ones. We conclude that behaviours which are, or appear, superstitious are an inevitable feature of adaptive behaviour in all organisms, including ourselves.