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Major evolutionary transitions (METs) across Earth's biological history describe fusions of lower-level entities into higher-level individuals (evolutionary transitions in individuality: ETIs) as well as novel forms of information storage and transmission (Information Leaps). Obligate eusociality is frequently listed as a MET—most often in the context of being an ETI and with an extrapolation that the ETI requires inclusive fitness maximization for all parties. However, obligate eusociality neither fundamentally alters how information is stored and transmitted nor meets the various criteria proposed for an ETI. We argue that rather than representing a higher-level individual, the evolution of non-reproductive worker castes is more analogous to a novel 'organ' that maintains homeostasis and nurtures the gonadal tissue of mated queens. Worker castes benefit queens by performing dangerous but necessary functions such as foraging, while enabling the gamete-producing functions to be kept relatively safe. This is an ecologically successful and significant evolutionary innovation, which can be thought of as a major competitive transition (MCT). In this context, we hypothesize that worker castes are most likely to evolve through parental manipulation. Employing such a MCT perspective generates a broad series of predictions about eusocial life histories. [ABSTRACT FROM AUTHOR]

When ants encounter a previously unexplored area, a variety of search patterns are possible. Previous studies have found that subsequent individuals tend to follow those that have gone before. This suggests that ants leave signature marks as they walk, independent of having encountered food, and that others recognize these and follow. This experiment tested if Argentine ants (Linepithema humile) also exhibit this pattern of behavior. Series of workers individually navigated through a grid consisting of two consecutive right-versus-left decisions. The resulting pattern does not significantly differ from random choice, as workers are neither more nor less likely to choose the path taken by a previous ant. The time between decisions also does not predict the path chosen. Either L. humile does not mark as they walk or workers do not use such marks in guiding their exploratory behavior. Under natural conditions, this suggests that L. humile is more expansive in initially distributing its workers across novel ground and less likely to have them clump together than species that do follow each other. This has implications for how the relative effectiveness in finding versus exploiting and defending food sites might vary across species. [ABSTRACT FROM AUTHOR]

The invasive success of the exotic Argentine ant [ Linepithema humile (Mayr)] is often closely tied to year-round availability of water sources. Previous studies suggest that the location of such water sources can strongly influence activity patterns of colonies and may be a key predictor of building infestations. We studied activity patterns of Argentine ants in relation to water and food resources in two open-air structures (aviaries). In one series of manipulations, ant activity inside the aviaries was significantly reduced with the placement of numerous water sources around the outside. Inside activity increased again when the outside water sources were removed. A second series of manipulations involved the placement of water sources at targeted locations outside of the structures. Ant activity inside the aviaries consistently shifted significantly closer to these targeted sites. The results suggest that providing a reliable water source to Argentine ant colonies exterior to buildings can be a non-chemical method of integrated pest management for reducing ant infestations. Independent of our manipulations, L. humile activity levels predictably declined with time of day, but these changes were uncorrelated with observed surface temperatures. In fact, activity was often noted at surface temperatures higher than those that cause worker mortality under laboratory conditions. This suggests that L. humile exhibits a consistent temperature-independent circadian activity pattern of reduced foraging in afternoons relative to mornings. [ABSTRACT FROM AUTHOR]

The authors discuss the implications of the exposure of foetus to untreated maternal depression and selective serotonin reuptake inhibitors (SSRIs) on neurodevelopment. Topics include the reproductive safety of SSRIs, the risk related to SSRIs exposure during pregnancy, and the association between SSRI exposure and disorders of language, speech, and neuromotor function in children.

Ant queens often cooperate in starting colonies (pleometrosis), but not all foundresses are likely to achieve equal reproductive success. Therefore, joining decisions may be influenced by queens' perceptions of a partner's likelihood to be of mutualistic benefit or to be a successful competitor in eventually controlling reproduction. Large queen size (as measured by weight) was assumed to be a desired characteristic in a mutualistic partner, but to be avoided in a potential competitor. With respect to this variable, Lasius pallitarsis queens appeared to join others in a manner consistent with increasing their competitive advantage. When given a choice between joining another queen or nesting alone, only queens with a large weight advantage were significantly likely to join. When given a choice between joining either a light or a heavy queen, queens of all weights preferentially joined the lighter resident. Moreover, when queen condition was improved by feeding, changes in joining behavior were consistent with predictions of improved competitive ability. Finally, lighter queens were more likely to leave nest sites when joined by others. However, queens significantly aggregated when in high densities, which may be consistent with gaining mutualistic benefits. Pleometrosis appears to have an evolutionary dynamic between mutualistic group benefits and individual competition to monopolize those benefits. [ABSTRACT FROM AUTHOR]

Lasius pallitarsis ants were placed in situations where they encountered unfamiliar areas and had to choose between one of two directions for further exploration. Workers advancing onto new ground apparently leave behind some chemical signature to which later ants orient. This orientation occurred under two types of experimental conditions. First, ants show a significant tendency to follow each other as they advance out from their colony into unexplored areas. The same ants transferred into an entirely novel situation, in which there is no obvious 'homeward' direction, show similar behavior. When ants are coming from familiar ground, following tends to increase as the number of ants passing the decision point increases. However, following decreases when ants are on entirely novel ground. The results are discussed in relation to models describing foraging responses. [ABSTRACT FROM AUTHOR]

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