Description of the male, nest architecture and biology notes of Zethus plaumanni Bohart & Stange, 1965 (Hymenoptera, Vespidae) in southern Brazil

Although diverse and widespread, there is much to improve on the knowledge of Zethus Fabricius, 1804 wasps. This includes aspects of many areas, such as data on taxonomy, behavior and biology. In the present study, we investigated Zethus plaumanni Bohart & Stange, 1965, a species hitherto known only from the female type in the literature, and worked to fill gaps on the knowledge of this species by describing the male and its genitalia, the nest structure and giving notes on the biology of individuals collected in trap-nests in southern Brazil. The male is diagnosable by characters also used for female identification. The nest follows the pattern of typical pre-existing cavity users, with a remarkable multi-layered nest plug. Sex ratio follows the 1:1 rule and sampling indicates diapause in the adult phase.

Natural history notes on worker size, colony size, and nest structure of Azteca muelleri Emery, 1893 (Hymenoptera: Formicidae) in Cecropia glaziovii (Rosales: Urticaceae) from the Atlantic Forest

Mutualistic association between Azteca Forel, 1878 ants and Cecropia Loefl. plants are one of the most studied interactions in Neotropics, however, natural history studies of Azteca species still poorly investigated due to the great effort required to conduct detailed descriptive studies. Here, we describe biological aspects of Azteca muelleri Emery, 1893 nesting in Cecropia glaziovii Snethl. in a fragment of Atlantic Forest, addressing (a) colony size; (b) nest distribution on the tree; and (c) worker and queen morphometrics. We collected two C. glaziovii saplings and counted characteristics of the nests and plants. We randomly selected 140 workers to measure and to determine whether intraspecific polymorphism occurs. Workers, immatures, and mealybugs were present in all hollow internodes of plant, and a queen was found. We found isometric morphological variation in A. muelleri. Our study provides new data to understand the biology of A. muelleri nesting in C. glaziovii, one of the most species-rich genera of arboreal ants known for the neotropics.

Modularity and connectivity of nest structure scale with colony size

Large body sizes have evolved structures to facilitate resource transport. Like unitary organisms, social insect colonies must transport information and resources, and colonies with more individuals may experience transport challenges similar to large-bodied organisms. In ant colonies, transport occurs in the nest, which may consist of structures that facilitate movement. We examine three attributes of nest structures that could mitigate transport challenges related to colony size: (1) subdivision: nests of species with large colonies are more subdivided to reduce viscosity of large crowds; (2) branching: nest tunnels increase branching in species with large colonies to reduce travel distances; and (3) short-cuts: nests of species with large colonies have cross-linking tunnels to connect distant parts of the nest and create alternative routes. We test these hypotheses by comparing nest structures of species with different colony sizes in phylogenetically controlled meta-analyses. Our findings support the subdivision and branching hypotheses. The nests of species with large colonies contain more, but not larger, chambers and reduce travel distances by increasing branching frequency. The similarity in how ant nests and the bodies of unitary organisms respond to increasing size suggests structural solutions that are common across levels of biological organization.

Nest Structure, Seasonality and Female Behavior of Epicharis (Anepicharis) dejeanii Lepeletier (Hymenoptera, Apidae, Centridini) in a Restinga Ecosystem, in Southern Brazil

We investigated the nesting behavior of females of Epicharis dejeanii and the architecture of their nests, in a large aggregation in a Restinga area, on Ilha do Superagui, southern Brazil. Surveys were carried out intermittently through the warm-wet seasons from different years between 2013 and 2017. The nest aggregation occupied an area of approximately 2,000 m2 and was situated on a sand bank and on flat sandy soil. Each nest consisted of a long unbranched tunnel, averaging 1.45 ± 0.35 m (N = 8), connected to a single brood cell with a mean length of 3.13 ± 0.2 cm (N = 13) and mean diameter of 1.2 ± 0.1 cm (N = 11). On average, females carried out 4.0 ± 2.4 foraging trips per day (N = 109) to collect floral resources for provisioning brood cells. Similar times were spent by females in their foraging trips for: only pollen (15.8 ± 14.3 min, N = 72), oil (22.5 ± 15.7 min, N = 45), or both resources (17.0 ± 15.1, N = 63). Our findings reveal that some variation in both nesting architecture and female behavior of E. dejeanii during nesting activities can occur in different locations from the same region.

Spatial asymmetry of the paternity success in nests of a fish with alternative reproductive tactics

Guard-sneaker tactics are widespread among fish, where territorial males defend a nest and provide parental care while sneakers try to steal fertilizations. Territorials and sneakers adopt diverse pre- and post-mating strategies, adjusting their ejaculate investment and/or behavioural responses to the presence of competitors. The relative distance of competitors from the spawning female plays a major role in influencing male mating strategies and the resulting paternity share. However, territorial male quality and sneaking intensity do not fully account for the variability in the relative siring success occurring among species. An often neglected factor potentially affecting sneakers proximity to females is the nest structure. We conducted a field experiment using the black goby, whose nests show two openings of different size. We found that territorial males defend more and sneaking pressure is higher at the front, larger access of the nest than at the back, smaller one. Moreover, microsatellite paternity analysis shows that territorials sire more offspring at the back of their nest. Such a predictable spatial distribution of the paternity share suggests that nest structure might work as an indirect cue of male relative siring success, potentially influencing the territorial male investment in parental care and/or the female egg deposition strategy.