Kate D. L. Umbers

Reversible colour change in Arthropoda

The mechanisms and functions of reversible colour change in arthropods are highly diverse despite, or perhaps due to, the presence of an exoskeleton. Physiological colour changes, which have been recorded in 90 arthropod species, are rapid and are the result of changes in the positioning of microstructures or pigments, or in the refractive index of layers in the integument. By contrast, morphological colour changes, documented in 31 species, involve the anabolism or catabolism of components (e.g. pigments) directly related to the observable colour. In this review we highlight the diversity of mechanisms by which reversible colour change occurs and the evolutionary context and diversity of arthropod taxa in which it has been observed. Further, we discuss the functions of reversible colour change so far proposed, review the limited behavioural and ecological data, and argue that the field requires phylogenetically controlled approaches to understanding the evolution of reversible colour change. Finally, we encourage biologists to explore new model systems for colour change and to engage scientists from other disciplines; continued cross‐disciplinary collaboration is the most promising approach to this nexus of biology, physics, and chemistry.

Ferocious Fighting between Male Grasshoppers

Contests among individuals over mating opportunities are common across diverse taxa, yet physical conflict is relatively rare. Due to the potentially fatal consequences of physical fighting, most animals employ mechanisms of conflict resolution involving signalling and ritualistic assessment. Here we provide the first evidence of ubiquitous escalated fighting in grasshoppers. The chameleon grasshopper (Kosciuscola tristis) is an Australian alpine specialist, in which males engage in highly aggressive combat over ovipositing females. We describe discrete agonistic behaviours including mandible flaring, mounting, grappling, kicking and biting, and their use depending on the individual’s role as challenger or defender. We show that male role predicts damage, with challengers being more heavily damaged than males defending females (defenders). Challengers also possess wider mandibles than defenders, but are similar in other metrics of body size. Our data suggest that fights escalate between males matched in body size and that mandibles are used as weapons in this species. This system represents an exciting opportunity for future research into the evolution of costly fighting behaviour in an otherwise placid group.

The Mothematics of Female Pheromone Signaling: Strategies for Aging Virgins

Although females rarely experience strong mate limitation, delays or lifelong problems of mate acquisition are detrimental to female fitness. In systems where males search for females via pheromone plumes, it is often difficult to assess whether female signaling is costly. Direct costs include the energetics of pheromone production and attention from unwanted eavesdroppers, such as parasites, parasitoids, and predators. Suboptimal outcomes are also possible from too many or too few mating events or near-simultaneous arrival of males who make unwanted mating attempts (even if successfully thwarted). We show that, in theory, even small costs can lead to a scenario where young females signal less intensely (lower pheromone concentration and/or shorter time spent signaling) and increase signaling effort only as they age and gather evidence (while still virgin) on whether sperm limitation threatens their reproductive success. Our synthesis of the empirical data available on Lepidoptera supports this prediction for one frequently reported component of signaling—time spent calling (often reported as the time of onset of calling at night)—but not for another, pheromone titer. This difference is explicable under the plausible but currently untested assumption that signaling earlier than other females each night is a more reliable way of increasing the probability of acquiring at least one mate than producing a more concentrated pheromone plume.

Colour in insect thermoregulation: Empirical and theoretical tests in the colour-changing grasshopper, Kosciuscola tristis

Body colours can result in different internal body temperatures, but evidence for the biological significance of colour-induced temperature differences is inconsistent. We investigated the relationship between body colour and temperature in a model insect species that rapidly changes colour. We used an empirical approach and constructed a heat budget model to quantify whether a colour change from black to turquoise has a role in thermoregulation for the chameleon grasshopper (Kosciuscola tristis). Our study shows that colour change in K. tristis provides relatively small temperature differences that vary greatly with wind speed (0.55 °C at ms(-1) to 0.05 °C at 10 ms(-1)). The biological significance of this difference is unclear and we discuss the requirement for more studies that directly test hypotheses regarding the fitness effects of colour in manipulating body temperature.

Prevalence and molecular identification of nematode and dipteran parasites in an Australian alpine grasshopper (Kosciuscola tristis)

In alpine Australia, Orthoptera are abundant, dominant herbivores, important prey species, and hosts for parasites and parasitoids. Despite the central role of orthopterans in alpine ecosystems, the impact of parasites on orthopteran populations is under-explored. In this study we describe the relationship between parasite prevalence and host sex, body size and year of collection. We accessed an existing, preserved collection of 640 Kosciuscola tristis collected from across its range between 2007 and 2011. Upon dissection we collected juvenile parasites and used molecular tools to identify them to three families (Nematoda; Mermithidae, and Arthropoda: Diptera: Tachinidae and Sarcophagidae). The prevalence of nematodes ranged from 3.5% to 25.0% and dipterans from 2.4% to 20.0%. Contrary to predictions, we found no associations between parasite prevalence and grasshopper sex or size. Although there was an association between prevalence of both nematodes and dipterans with year of collection, this is likely driven by a small sample size in the first year. Our results provide a foundation for future studies into parasite prevalence within the alpine environment and the abiotic factors that might influence these associations.

Reproducible research in the study of biological coloration

The study of colour in nature has generated insights intofundamental evolutionary and ecological processes, and researchinto colour traits is a rapidly growing field (Kelber & Osorio, 2010).Theongoinginterestinbiologicalcolorationhasinpartbeendrivenby the increased availability of key technologies, including spec-trometry and photography, and concurrent advances in methodsfor analysing colour data, such as visual models (e.g. Endler M Kelber, Vorobyev, & Osorio, 2003; Stevens, Parraga,Cuthill, Partridge, & Troscianko, 2007). While these developmentsare positive for the field, the increasingly complex analyses beingrun on ever greater amounts of data heighten the need forcomprehensive methods reporting and diligent data management(Alsheikh-Ali, Qureshi, Al-Mallah, & Ioannidis, 2011; Nekrutenko T Van Noorden, 2011; Whitlock, 2011). Astudy may be considered truly reproducible when it satisfies threebroad criteria: (1) methods are reported completely, (2) data arepubliclyavailable and archived,and (3) the chain of modification ofraw data is documented and preserved. While completely repro-ducible research (e.g. FitzJohn et al., 2014) is a laudable goal, theconsiderable demands it imposes on researchers means that it willoften, in practice, be unattainable. Nevertheless, even partialreproducibility through the relatively simple practices of completemethodsreportingandpublicdataarchivingisoftremendousvalue.Our aim was to explore the state of reproducibility in the studyofbiological coloration, and to suggest simpleways inwhich it maybe improved. We first outline common methods for studying bio-logical coloration and present guidelines for comprehensivemethods reporting. We then explore how well some of theseimportant criteria have been reported in the literature. We alsoquantify the availability of publicly archived data and code andsuggest some useful tools for increasing the reproducibility ofcolour trait research more broadly.

The Effects of Residency and Body Size on Contest Initiation and Outcome in the Territorial Dragon, Ctenophorus decresii

Empirical studies of the determinants of contests have been attempting to unravel the complexity of animal contest behaviour for decades. This complexity requires that experiments incorporate multiple determinants into studies to tease apart their relative effects. In this study we examined the complex contest behaviour of the tawny dragon (Ctenophorus decresii), a territorial agamid lizard, with the specific aim of defining the factors that determine contest outcome. We manipulated the relative size and residency status of lizards in contests to weight their importance in determining contest outcome. We found that size, residency and initiating a fight were all important in determining outcomes of fights. We also tested whether residency or size was important in predicting the status of lizard that initiated a fight. We found that residency was the most important factor in predicting fight initiation. We discuss the effects of size and residency status in context of previous studies on contests in tawny dragons and other animals. Our study provides manipulative behavioural data in support of the overriding effects of residency on initiation fights and winning them.

Turn the temperature to turquoise: Cues for colour change in the male chameleon grasshopper (Kosciuscola tristis) (Orthoptera: Acrididae)

Rapid, reversible colour change is unusual in animals, but is a feature of male chameleon grasshoppers (Kosciuscola tristis). Understanding what triggers this colour change is paramount to developing hypotheses explaining its evolutionary significance. In a series of manipulative experiments the author quantified the effects of temperature, and time of day, as well as internal body temperature, on the colour of male K. tristis. The results suggest that male chameleon grasshoppers change colour primarily in response to temperature and that the rate of colour change varies considerably, with the change from black to turquoise occurring up to 10 times faster than the reverse. Body temperature changed quickly (within 10min) in response to changes in ambient temperature, but colour change did not match this speed and thus colour is decoupled from internal temperature. This indicates that male colour change is driven primarily by ambient temperature but that their colour does not necessarily reflect current internal temperature. I propose several functional hypotheses for male colour change in K. tristis.

Molecular phylogeny of the Kosciuscola grasshoppers endemic to the Australian alpine and montane regions

Abstract. Diversity and speciation in Australia’s alpine biota are poorly understood. Here we present a molecular phylogeny of the Australian alpine grasshopper genus Kosciuscola (Sjösted) that currently includes five described species. These grasshoppers are of interest not only because of their alpine distribution but also for the extraordinary colour change exhibited by the species K. tristis, whose males turn turquoise when their body temperature exceeds 25°C. We reconstructed the phylogeny with two fragments of the mitochondrial genome using parsimony, maximum likelihood and Bayesian analyses and our data support the current taxonomy. Further, our data show little geographic structuring within some clades, which is puzzling since members of Kosciuscola are brachypterous. Finally, our data coupled with our observations on colouration provide evidence for a genetically distinct clade of K. tristis in the Victorian Alps. This is among the first molecular studies of an alpine invertebrate and one of a few on non-endangered, widespread Australian alpine species. More phylogenetic studies in the Australian Alps are required if we are to understand the evolution of alpine fauna and establish baseline data to monitor their response to climate change.

Deimatism: a neglected component of antipredator defence

Deimatic or ‘startle’ displays cause a receiver to recoil reflexively in response to a sudden change in sensory input. Deimatism is sometimes implicitly treated as a form of aposematism (unprofitability associated with a signal). However, the fundamental difference is, in order to provide protection, deimatism does not require a predator to have any learned or innate aversion. Instead, deimatism can confer a survival advantage by exploiting existing neural mechanisms in a way that releases a reflexive response in the predator. We discuss the differences among deimatism, aposematism, and forms of mimicry, and their ecological and evolutionary implications. We highlight outstanding questions critical to progress in understanding deimatism.