RESUMO
Habitat fragmentation is considered an important threat to biodiversity, increasing species exposure to edge effects. The Brazilian Cerrado savanna is considered a biodiversity hotspot and has been converted to small, isolated fragments due to human activities. Ant communities and colony survivorship are known to be affected by edge effects in Cerrado, but to date there is no information on the genetic diversity of ant colonies at the edge of fragmented areas. Here, we investigate if colony genetic diversity and structure of Odontomachus chelifer (Latreille) ants (Hymenoptera: Formicidae) are subject to edge effects in a Cerrado reserve in southeast Brazil. Using microsatellites, we evaluated the number of breeders (queens and males) and the genetic diversity in O. chelifer colonies located in the interior versus edge of a Cerrado fragment. All O. chelifer nests had multiple queens, which presented a low mating frequency. The number of breeders and most estimates of genetic diversity did not differ between colonies at the edge versus interior of the fragment. Genetic structure was not influenced by nest location as well. However, we detected a small and positive increase in the observed heterozygosity in colonies located at fragment edges. High heterozygosity is thought to be particularly important in fast-changing environments, such as edges, providing an advantage for genetic diversity. Further investigation is needed to assess in greater detail how habitat loss affects O. chelifer biology. Our study is a first step toward elucidating edge effects on genetic diversity of ant colonies, a topic still poorly explored in tropical environments.
Assuntos
Formigas , Humanos , Animais , Formigas/genética , Pradaria , Brasil , Ecossistema , Variação GenéticaRESUMO
A better knowledge of the behaviors that reduce traffic congestions is essential to understand the success of the trail system despite of costs. Leaf-cutting ants use a trunk-trail system to transport leaf fragments into their nests. Some ants carry extra-large leaf fragments and walk slower than the rest of laden workers, thus slowing the ant column behind them. Here we experimentally address whether fragment size selection by leaf-cutting ants depends on the foraging ant flow. If ant behavior aims at minimizing delays associated with carrying extra-large loads, we expect that extra-large loads will be selected mostly under low ant flow conditions. In 38 foraging trails from 18 nests of Acromyrmex crassipinus located in Chaco Serrano woodland, Argentina, we recorded the removal of medium and extra-large baits under variable ant flow conditions. Ants selected extra-large loads mainly under low flow conditions; the increment of ant flow caused an exponential decrease in the proportion and in the preference to carry extra-large fragments. Restriction of heavy vehicles during peak hours is a common traffic rule that prevents traffic jams in transport networks. Our results suggest that this rule may also apply in ant societies that use foraging trails. Avoiding delays generated by carrying large loads appear to be another reason to transport leaf fragments below the individual load capacity, which might help to better understand the high variation in load sizes carried by leaf-cutting ants. This work might help to explain how by following simple traffic rules the trail system can be successful despite its costs, and also illustrate how individual ant behavior can be influenced by nestmates, thereby improving resource harvest in the colony as a whole.
Assuntos
Formigas/fisiologia , Comportamento Alimentar/psicologia , Animais , Feminino , Masculino , Comportamento de Nidação , Folhas de Planta , Percepção de Tamanho , CaminhadaRESUMO
Anurans have three primary types of locomotion: walking, jumping, and swimming. Additionally, they may dig, climb, grasp, etc. All adult anurans have four limbs, with four fingers on the hands and five toes on the feet. We summarized and updated knowledge on the interspecific variation within anuran limbs, then discuss how developmental constraints (e.g., in size) and novelties may have influenced anuran diversification through the locomotion. We analyze morphological variation from limb bud stages up to the final limb form resulting from certain skeletal organization and growth. We find limited morphometric variations in the skeleton of different developmental modules (i.e., skull, trunk, urostyle, limbs) indicate that the anuran body shape is largely constrained. We identify specializations of the stylopodium, zeugopodium, and proximal carpals/tarsals that have evolved to facilitiate saltatorial locomotion. We show that the anuran prepollex and prehallux are not vestigial digits and that they have come to serve specialized function. Medial rotation of the manus in anurans appears to have evolved to help distribute the force of impact upon landing at the end of a jump. Additional skeletal elements in anuran limbs are intercalary elements and sesamoids. The intercalary elements appear within neobatrachians and are integrated with digital pads in lineages capable of locomotion on smooth vertical surfaces. They have allowed arboreal anurans to occupy a wide range of arboreal habitats.