The Evolution of Rodent Tail Morphology.

AbstractPopulation-level variation in rodent tail structures has been variously attributed to facilitating social communication, locomotion, thermoregulation, and predator avoidance. Little is known, however, about the applicability of these ecological and social correlates to explaining the tremendous interspecific diversity of this appendage. To investigate the potential drivers of rodent tail morphology at a macroevolutionary level, we first carefully reviewed the literature and constructed a list of major hypotheses regarding this variation. We then compiled a database of 11 different tail traits related to length, color, texture, and ecological characteristics for 2,101 species of rodents (order Rodentia) and examined their key evolutionary correlates. Using Bayesian phylogenetic mixed models across the entire order and additionally within the five rodent suborders, we found that tail length is correlated with both temperature (Allen's rule) and locomotory mode, that black tips are more common in brightly lit environments, that naked tails are often found in warmer climates, that fluffy-tipped tails are more common in smaller and/or arboreal species, that prehensility is predominant in arboreal species and/or species with longer tails, and that tail autotomy is more common in open environments. Most of our tested predictions, largely drawn from population-level studies, are not recapitulated across the entire order, potentially indicating a role of local ecological context in shaping tail morphology.

Outstanding issues in the study of antipredator defenses.

Protective defense mechanisms are well documented across the animal kingdom, but there are still examples of antipredator defenses that do not fit easily into the current conceptualization. They either fall within the intersection of multiple mechanisms or fail to fall neatly into pre-existing categories. Here, using Endler's predatory sequence as a framework, we identify problematic examples of antipredator defenses, separating them into protective mechanisms that are difficult to classify and those which act sequentially depending on context. We then discuss three ways of improving underlying terminological and definitional problems: (1) issues with English and polysemy, (2) overlapping aspects of similar mechanisms, and (3) unclear definitions. By scrutinizing the literature, we disentangle several opaque areas in the study of protective defense mechanisms and highlight questions that require further research. An unclear conceptual framework for protective defense mechanisms can lead to misconceptions in understanding the costs and benefits of defenses displayed by animals, while interchangeable terminologies and ambiguous definitions can hinder communication in antipredator studies.

Predation risk drives aposematic signal conformity.

Contrary to expectations regarding efficient predator education mediated by lack of ambiguity and enhanced prey recognition, aposematic signals often show considerable intraspecific variability. For example, some striped skunks (Mephitis mephitis) are almost entirely white, others have black-and-white stripes of equivalent thicknesses, yet others are mostly black. We tested the ecological correlates of this variation in patterning using 749 museum skins collected across North America. Skunks had longer white-black borders and more bilaterally symmetrical stripes in areas with a greater number of potential predator species, and this effect was more marked for mammalian than avian predators, the latter of which may be less deterred by noxious defenses. Skunks from locations with greater predator diversity were less variable in the extent of whiteness on their dorsa and less variable in the length of their white-black borders, suggesting strong selection from predators leads to greater conformity in stripe patterns, even at the same location, but weak selection from predators leads to relaxed selection on pattern conformity. Skunks exhibited greater areas of black pelage in areas of greater humidity conforming to Gloger's rule. Our results indicate that relaxed predation pressure is key to warning signal variation in this iconic species, whereas stronger pressure leads to signal conformity and stronger signals.

Bear essentials.

Strangely, American black bears come in many colours. New work by Puckett et al. shows that a missense alteration in the gene encoding tyrosinase-related protein 1 (TYRP1) likely interferes with melanin synthesis and is responsible for the cinnamon colour variant in the southwest USA. However, the adaptive significance of colour polymorphisms in this large carnivore remains opaque.

Why don't horseflies land on zebras?

Stripes deter horseflies (tabanids) from landing on zebras and, while several mechanisms have been proposed, these hypotheses have yet to be tested satisfactorily. Here, we investigated three possible visual mechanisms that could impede successful tabanid landings (aliasing, contrast and polarization) but additionally explored pattern element size employing video footage of horseflies around differently patterned coats placed on domestic horses. We found that horseflies are averse to landing on highly but not on lightly contrasting stripes printed on horse coats. We could find no evidence for horseflies being attracted to coats that better reflected polarized light. Horseflies were somewhat less attracted to regular than to irregular check patterns, but this effect was not large enough to support the hypothesis of disrupting optic flow through aliasing. More likely it is due to attraction towards larger dark patches present in the irregular check patterns, an idea bolstered by comparing landings to the size of dark patterns present on the different coats. Our working hypothesis for the principal anti-parasite features of zebra pelage are that their stripes are sharply outlined and thin because these features specifically eliminate the occurrence of large monochrome dark patches that are highly attractive to horseflies at close distances.

Practical guide to coproduction in conservation science.

We considered a series of conservation-related research projects on the island of Pemba, Tanzania, to reflect on the broad significance of Beier et al.'s recommendations for linking conservation science with practical conservation outcomes. The implementation of just some of their suggestions can advance a successful coproduction of actionable science by small research teams. Key elements include, first, scientists and managers working together in the field to ensure feedback in real time; second, questions jointly identified by managers and researchers to facilitate engaged collaboration; third, conducting research at multiple sites, thereby broadening managers' abilities to reach multiple stakeholders; and fourth, establishing a multidisciplinary team because most of the concerns of local managers require input from multiple disciplines.

Consideramos una serie de proyectos de investigación relacionados con la conservación en la isla de Pemba, Tanzania, para reflexionar sobre la importancia de las recomendaciones de Beier et al. para vincular las ciencias de la conservación con sus resultados prácticos. La implementación de sólo algunas de sus sugerencias puede impulsar una coproducción exitosa de ciencia práctica hecha por pequeños equipos de investigación. Los elementos clave incluyen, primero, a los científicos y administrados trabajando juntos en el campo para asegurar respuestas en tiempo real; segundo, preguntas identificadas en conjunto por los administradores y los investigadores para facilitar la colaboración participativa; tercero, realizar investigaciones en sitios diferentes y ampliar con esto las habilidades de los administradores para llegar a múltiples actores; y cuarto, establecer un equipo multidisciplinario ya que la mayoría de los intereses de los administradores locales requieren información de múltiples disciplinas.

The giant panda is cryptic.

The giant panda (Ailuropoda melanoleuca) is an iconic mammal, but the function of its black-and-white coloration is mysterious. Using photographs of giant pandas taken in the wild and state-of-the-art image analysis, we confirm the counterintuitive hypothesis that their coloration provides camouflage in their natural environment. The black fur blends into dark shades and tree trunks, whereas white fur matches foliage and snow when present, and intermediate pelage tones match rocks and ground. At longer viewing distances giant pandas show high edge disruption that breaks up their outline, and up close they rely more on background matching. The results are consistent across acuity-corrected canine, feline, and human vision models. We also show quantitatively that the species animal-to-background colour matching falls within the range of other species that are widely recognised as cryptic. Thus, their coloration is an adaptation to provide background matching in the visual environment in which they live and simultaneously to afford distance-dependent disruptive coloration, the latter of which constitutes the first computational evidence of this form of protective coloration in mammals.

Aposematism in mammals.

Aposematic coloration is traditionally considered to signal unpalatability or toxicity. In mammals, most research has focused on just one form of defense, namely, noxious anal secretions, and its black-and-white advertisement as exemplified by skunks. The original formulation of aposematism, however, encompassed a broader range of morphological, physiological, and behavioral defenses, and there are many mammal species with black-and-white contrasting patterns that do not have noxious adaptations. Here, using Bayesian phylogenetic models and data from 1726 terrestrial nonvolant mammals we find that two aspects of conspicuous coloration, black-and-white coloration patterns on the head and body, advertise defenses that are morphological (spines, large body size), behavioral (pugnacity), and physiological (anal secretions), as well as being involved with sexual signaling and environmental factors linked to crypsis. Within Carnivora, defensive anal secretions are associated with complex black-and-white head patterns and longitudinal black-and-white body striping; in primates, larger bodied species exhibit irregular patches of black-and-white pelage; and in rodents, pugnacity is linked to sharp countershading and irregular blocks of white and black pelage. We show that black-and-white coloration in mammals is multifunctional, that it serves to warn predators of several defenses other than noxious anal secretions, and that aposematism in mammals is not restricted to carnivores.

Towards an ecology of protective coloration.

The strategies underlying different forms of protective coloration are well understood but little attention has been paid to the ecological, life-history and behavioural circumstances under which they evolve. While some comparative studies have investigated the ecological correlates of aposematism, and background matching, the latter particularly in mammals, few have examined the ecological correlates of other types of protective coloration. Here, we first outline which types of defensive coloration strategies may be exhibited by the same individual; concluding that many protective coloration mechanisms can be employed simultaneously, particularly in conjunction with background matching. Second, we review the ecological predictions that have been made for each sort of protective coloration mechanism before systematically surveying phylogenetically controlled comparative studies linking ecological and social variables to antipredator defences that involve coloration. We find that some a priori predictions based on small-scale empirical studies and logical arguments are indeed supported by comparative data, especially in relation to how illumination affects both background matching and self-shadow concealment through countershading; how body size is associated with countershading, motion dazzle, flash coloration and aposematism, although only in selected taxa; how immobility may promote background matching in ambush predators; and how mobility may facilitate motion dazzle. Examination of nearly 120 comparative tests reveals that many focus on ecological variables that have little to do with predictions derived from antipredator defence theory, and that broad-scale ecological studies of defence strategies that incorporate phylogenetics are still very much in their infancy. We close by making recommendations for future evolutionary ecological research.

Zebra stripes.

Tim Caro introduces why zebras are striped.

Zebra stripes, tabanid biting flies and the aperture effect.

Of all hypotheses advanced for why zebras have stripes, avoidance of biting fly attack receives by far the most support, yet the mechanisms by which stripes thwart landings are not yet understood. A logical and popular hypothesis is that stripes interfere with optic flow patterns needed by flying insects to execute controlled landings. This could occur through disrupting the radial symmetry of optic flow via the aperture effect (i.e. generation of false motion cues by straight edges), or through spatio-temporal aliasing (i.e. misregistration of repeated features) of evenly spaced stripes. By recording and reconstructing tabanid fly behaviour around horses wearing differently patterned rugs, we could tease out these hypotheses using realistic target stimuli. We found that flies avoided landing on, flew faster near, and did not approach as close to striped and checked rugs compared to grey. Our observations that flies avoided checked patterns in a similar way to stripes refutes the hypothesis that stripes disrupt optic flow via the aperture effect, which critically demands parallel striped patterns. Our data narrow the menu of fly-equid visual interactions that form the basis for the extraordinary colouration of zebras.

Coloration in Mammals.

Mammalian colors and color patterns are some of the most diverse and conspicuous traits found in nature and have been widely studied from genetic/developmental and evolutionary perspectives. In this review we first discuss the proximate causes underlying variation in pigment type (i.e., color) and pigment distribution (i.e., color pattern) and highlight both processes as having a distinct developmental basis. Then, using multiple examples, we discuss ultimate factors that have driven the evolution of coloration differences in mammals, which include background matching, intra- and interspecific signaling, and physiological influences. Throughout, we outline bridges between developmental and functional investigatory approaches that help broaden knowledge of mammals' memorable external appearances, and we point out areas for future interdisciplinary research.

Can behavioural ecologists help establish protected areas?

Protecting wild places is conservation's most pressing task given rapid contemporary declines in biodiversity and massive land use changes. We suggest that behavioural ecology has a valuable, albeit limited, role to play in this agenda. Behaviourally based empiricism and modelling, especially of animal movements and habitat preferences have enjoyed wide applicability in delineating reserve boundaries. In protected areas that sanction exploitation, it may also be important to understand individuals' behavioural and life-history responses to management decisions. We also argue, however, that the in-depth studies of behavioural ecologists may have an important role in conservation by elevating species' status from mundane to charismatic and often sparking public empathy, and their mere presence in field generates local (or broader) intrigue. More generally behavioural ecologists will only be listened to, and their contributions considered of conservation importance, if they become more involved in decision-making processes as witnessed by several prominent examples that have supported the establishment of protected areas. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.

Aposematism: Unpacking the Defences.

Aposematic coloration is commonly considered to signal unpalatability, yet animals advertise malodour, spines, and weaponry as well as toxins, some of which can be seen at a distance whereas others are hidden from predators. Separating defences into overt and covert categories in this way and whether they act before, during contact, or following ingestion generates new insights into the evolution of aposematism. Signals drawing attention to overt defences are difficult to fake whereas signals advertising covert defences can deceive would-be predators, and those acting later in the predatory sequence are more likely to be dishonest. These two orthogonal defence categorizations help to frame where dishonest signalling occurs in nature, set limits on deception by dishonest Batesian mimics, and prompt new questions.

Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses.

Averting attack by biting flies is increasingly regarded as the evolutionary driver of zebra stripes, although the precise mechanism by which stripes ameliorate attack by ectoparasites is unknown. We examined the behaviour of tabanids (horse flies) in the vicinity of captive plains zebras and uniformly coloured domestic horses living on a horse farm in Britain. Observations showed that fewer tabanids landed on zebras than on horses per unit time, although rates of tabanid circling around or briefly touching zebra and horse pelage did not differ. In an experiment in which horses sequentially wore cloth coats of different colours, those wearing a striped pattern suffered far lower rates of tabanid touching and landing on coats than the same horses wearing black or white, yet there were no differences in attack rates to their naked heads. In separate, detailed video analyses, tabanids approached zebras faster and failed to decelerate before contacting zebras, and proportionately more tabanids simply touched rather than landed on zebra pelage in comparison to horses. Taken together, these findings indicate that, up close, striped surfaces prevented flies from making a controlled landing but did not influence tabanid behaviour at a distance. To counteract flies, zebras swished their tails and ran away from fly nuisance whereas horses showed higher rates of skin twitching. As a consequence of zebras' striping, very few tabanids successfully landed on zebras and, as a result of zebras' changeable behaviour, few stayed a long time, or probed for blood.