Individuals are often consistent in their behavior but vary from each other in the level of behavior shown. Despite burgeoning interest in such animal personality variation, studies on invertebrates are scarce, and studies on clonal invertebrates nonexistent. This is surprising given the obvious advantages of using invertebrates/clones to tackle the crucial question why such consistent behavioral differences exist. Here we show that individuals of clonal pea aphids exhibit consistent behavioral differences in their escape responses to a predator attack (dropping vs. nondropping off a plant). However, behavior was not repeatable at the clonal level. Genetically identical clones expressed various phenotypes but different clones produced different proportions of each phenotype (dropper, nondropper, and inconsistent). Manipulations of early environmental conditions had little qualitative impact on such patterns. We discuss the importance of our findings for future studies of the evolutionary and ecological consequences of personality variation.

We found that both apes generally had the same grip preferences and used similar forelimb postures on supports of a similar size, which is consistent with their overall similarity in hard and soft tissue morphology of the hand and forelimb. However, some species-specific differences in morphology appear to elicit slightly different grasping strategies during vertical climbing between mountain gorillas and chimpanzees.

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Summary1. Life-history trade-offs are considered a major driving force in the emergence of consistent behavioural differences (personality variation); but empirical tests are scarce. 2. We investigated links between a personality trait (escape response), life-history and state variables (growth rate, size and age at first reproduction, age-dependent reproductive rates, lifetime reproductive success, life span) in red and green colour morphs of clonal pea aphids, Acyrthosiphon pisum. Escape response (dropping/non-dropping off a plant upon a predatory attack) was measured repeatedly to classify individuals as consistent droppers, consistent nondroppers or inconsistents. 3. Red morphs experienced stronger trade-offs between early reproduction and life span than green morphs; and red consistent (non)droppers had highest lifetime reproductive success. Red droppers followed a risk-averse life-history strategy (high late reproduction), red nondroppers a risk-prone strategy (high early reproduction), while reproductive rates were equivalent for all green behavioural types and red inconsistents. 4. This suggests that red morphs suffer the highest costs of dropping (they are most conspicuous to predators), which 'equivalates' fitness payoffs to both risk-takers (red non-droppers) and risk-averse red droppers. The strong trade-off also means that committing to a particular lifestyle (being consistent) maximises fitness. 5. Our study suggests that life-history trade-offs likely mediate personality variation but effects might depend on interactions with other organismal characteristics (here: colour morph).

Biomechanical analyses of arboreal locomotion in great apes in their natural environment are scarce and thus attempts to correlate behavioral and habitat differences with variations in morphology are limited. The aim of this study was to investigate the gait characteristics of vertical climbing in mountain gorillas (Gorilla beringei beringei) and chimpanzees (Pan troglodytes) in a natural environment to assess differences in the climbing styles that may relate to variation in body size. We investigated temporal variables (i.e., cycle duration, duty factors, and stride frequency) and footfall sequences (i.e., diagonal vs. lateral sequence gaits) during vertical climbing (both ascent and descent) in 11 wild mountain gorillas and compared these data to those of eight semi-free-ranging chimpanzees, using video records ad libitum. Comparisons of temporal gait parameters revealed that large-bodied mountain gorillas exhibited a longer cycle duration, lower stride frequency and generally a higher duty factor than small-bodied chimpanzees. While both apes were similarly versatile in their vertical climbing performance in the natural environment, mountain gorillas most often engaged in diagonal sequence/diagonal couplet gaits and chimpanzees most often used lateral sequence/diagonal couplet gaits. This study revealed that mountain gorillas adapt their climbing strategy to accommodate their large body mass in a similar manner previously found in captive western lowland gorillas, and that chimpanzees are less variable in their climbing strategy than has been documented in captive bonobos.