Silky sifaka (Propithecus candidus) use sleep sites for thermoregulation, food access and predator avoidance

Primate sleeping site selection is influenced by multiple ecological factors including predation avoidance, thermoregulation, and food access. To test these hypotheses, we studied the sleeping trees used by a group of wild silky sifakas (Propithecus candidus) in Marojejy National Park, Madagascar. During this ten-month study, the group slept in 828 sleeping trees from approximately 35 genera. In support of thermoregulation, generalised linear models revealed that as temperature decreased, the number of individuals sleeping together significantly increased and they slept at further distances from the trunk. As rainfall increased, sleep site height significantly increased. Weinmannia was the most frequented tree genus, despite low abundance, accounting for 29% of all sleeping trees. In support of food access, 94.8% of sleeping trees were food trees. Weinmannia is among the most highly preferred food trees. The group slept at a mean height of 16.0 m near the top of tall trees which averaged 19.5 m. Sleep trees were significantly taller than trees in botanical plots within the sifaka’s home range. They never slept in the same trees on consecutive nights, and sleeping heights were significantly higher than daytime heights which is consistent with predation avoidance. Social sleeping in groups of two or three individuals (62.9%) was more common than solitary sleeping (37.1%). At such heights, huddling may increase vigilance and lessen the risk of predation by the fossa (Cryptoprocta ferox) while also reducing heat loss. These patterns suggest that silky sifaka sleep site choice is influenced by thermoregulation and food access in addition to predation avoidance. We suggest that understanding sleep site use can assist in conservation of species like silky sifakas by enabling researchers to find new groups, protect habitats with key tree species, and inform reforestation efforts.

Parasite infection disrupts escape behaviours in fish shoals

Many prey species have evolved collective responses to avoid predation. They rapidly transfer information about potential predators to trigger and coordinate escape waves. Predation avoidance behaviour is often manipulated by trophically transmitted parasites, to facilitate their transmission to the next host. We hypothesized that the presence of infected, behaviourally altered individuals might disturb the spread of escape waves. We used the tapeworm Schistocephalus solidus , which increases risk-taking behaviour and decreases social responsiveness of its host, the three-spined stickleback, to test this hypothesis. Three subgroups of sticklebacks were placed next to one another in separate compartments with shelter. The middle subgroup contained either uninfected or infected sticklebacks. We confronted an outer subgroup with an artificial bird strike and studied how the escape response spread through the subgroups. With uninfected sticklebacks in the middle, escape waves spread rapidly through the entire shoal and fish remained in shelter thereafter. With infected sticklebacks in the middle, the escape wave was disrupted and uninfected fish rarely used the shelter. Infected individuals can disrupt the transmission of flight responses, thereby not only increasing their own predation risk but also that of their uninfected shoal members. Our study uncovers a potentially far-reaching fitness consequence of grouping with infected individuals.

The evolution of coloration and opsins in tarantulas

Tarantulas paradoxically exhibit a diverse palette of vivid coloration despite their crepuscular to nocturnal habits. The evolutionary origin and maintenance of these colours remains mysterious. In this study, we reconstructed the ancestral states of both blue and green coloration in tarantula setae, and tested how these colours correlate with presence of stridulation, urtication and arboreality. Green coloration has probably evolved at least eight times, and blue coloration is probably an ancestral condition that appears to be lost more frequently than gained. While our results indicate that neither colour correlates with the presence of stridulation or urtication, the evolution of green coloration appears to depend upon the presence of arboreality, suggesting that it ptobably originated for and functions in crypsis through substrate matching among leaves. We also constructed a network of opsin homologues across tarantula transcriptomes. Despite their crepuscular tendencies, tarantulas express a considerable diversity of opsin genes—a finding that contradicts current consensus that tarantulas have poor colour vision on the basis of low opsin diversity. Overall, our findings raise the possibility that blue coloration could have ultimately evolved via sexual selection and perhaps proximately be used in mate choice or predation avoidance due to possible sex differences in mate-searching.

Bacterial mobbing behavior: coordinated communal attack of Pseudomonas aeruginosa on a protozoan predator

Mobbing, a group attack of prey on predator, is a strategy enacted by many animal species. Here we report bacterial mobbing carried out by the bacterium Pseudomonas aeruginosa towards Acanthamoeba castellanii, a common bacterivore. This behavior consists of bacterial taxis towards the amoebae, adhesion en masse to amoebae cells, and eventual killing of the amoebae. Mobbing behavior transpires in second’s timescale and responds to predator population density. A mutant defective in the production of a specific quorum sensing signal displays reduced adhesion to amoeba cells. This deficiency ameliorated by external addition of the missing signal molecule. The same quorum sensing mutant also expresses long term deficiency in its ability to cause amoeba death and shows higher susceptibility to predation, highlighting the importance of group coordination to mobbing and predation avoidance. These findings portray bacterial mobbing as a regulated and dynamic group behavior.

The Evolution Of Colouration And Opsins In Tarantulas

ABSTRACTTarantulas paradoxically exhibit a diverse palette of vivid colouration despite their crepuscular to nocturnal habits. The evolutionary origin and maintenance of these colours remains a mystery. In this study, we reconstructed the ancestral states of both blue and green colouration in tarantula setae, and tested how these colours correlate with the presence of stridulation, urtication, and arboreality. Green colouration has likely evolved at least eight times, and blue colouration is likely an ancestral condition that appears to be lost more frequently than gained. While our results indicate that neither colour correlates with the presence of stridulation or urtication, the evolution of green colouration appears to depend upon the presence of arboreality, suggesting that it likely originated for, and functions in, crypsis through substrate matching among leaves. We also constructed a network of opsin homologs across tarantula transcriptomes. Despite their crepuscular tendencies, tarantulas express a full suite of opsin genes – a finding that contradicts current consensus that tarantulas have poor colour vision on the basis of low opsin diversity. Overall, our results support the intriguing hypotheses that blue colouration may have ultimately evolved via sexual selection and perhaps proximately be used in mate choice or predation avoidance due to possible sex differences in mate-searching.

Disruptive coloration and habitat use by seahorses

ABSTRACT Predation avoidance is a primary factor influencing survival. Therefore, any trait that affects the risk of predation, such as camouflage, is expected to be under selection pressure. Background matching (homochromy) limits habitat use, especially if the habitat is heterogeneous. Another camouflage mechanism is disruptive coloration, which reduces the probability of detection by masking the prey’s body contours. Here we evaluated if disruptive coloration in the longsnout seahorse, Hippocampus reidi, allows habitat use diversification. We analyzed 82 photographs of animals, comparing animal and background color, and registering anchorage substrate (holdfast). We tested whether the presence (disruptive coloration) or absence of bands (plain coloration) predicted occupation of backgrounds of different colors. We also calculated the connectance between seahorse morph and background color or holdfast, as well as whether color morph differed in their preferences for holdfast. Animals with disruptive coloration were more likely to be found in environments with colors different from their own. Furthermore, animals with disruptive coloration occupied more diversified habitats, but as many holdfasts as plain colored animals. Therefore, animals with disruptive coloration were less selective in habitat use than those lacking disruptive color patterns, which agrees with the disruptive coloration hypothesis.

Anophtalmic and epigean? Description of an intriguing new species of Hyalella (Amphipoda, Hyalellidae) from Brazil

The absence of eyes in Hyalella (Hyalellidae, Amphipoda) is typical of obligate groundwater-dwelling species. However, a new intriguing blind amphipod of this genus was found in epigean streams from the Iron Quadrangle (state of Minas Gerais, Brazil). Hyalella troglofugia sp nov. presents antenna 1 shorter than antenna 2, gnathopod 1 propodus inner face with four setae, gnathopod 2 propodus posterior margin longer than palm, dactylus slightly longer than palm, pereopod 5 shorter than others and uropod 3 shorter than telson. The absence of eyes and presence of reduced U3 and pereopods of H. troglofugia sp nov. may suggest that such species also inhabits interstitial subterranean spaces. Moreover, the presence of the new species on streams associated to distinct hydrological zones indicates that this species may be present in different types of subterranean habitats of the region. We hypothesize that at least part of the population of this species may have left the subterranean environment looking for food and when out of this habitat it preferentially inhabits high water flow stretches of the stream in function of predation avoidance.

Estimating the age of Heliconius butterflies from calibrated photographs

Mating behaviour and predation avoidance in Heliconius involve visual colour signals; however, there is considerable inter-individual phenotypic variation in the appearance of colours. In particular, the red pigment varies from bright crimson to faded red. It has been thought that this variation is primarily due to pigment fading with age, although this has not been explicitly tested. Previous studies have shown the importance of red patterns in mate choice and that birds and butterflies might perceive these small colour differences. Using digital photography and calibrated colour images, we investigated whether the hue variation in the forewing dorsal red band of Heliconius melpomene rosina corresponds with age. We found that the red hue and age were highly associated, suggesting that red colour can indeed be used as a proxy for age in the study of wild-caught butterflies.