Visual Signalling in Plant-Animal Interactions

<p>The process of visual signalling between plant and animals is often a combination of exciting discoveries and more often than not; highly controversial hypotheses. Plants and animals interact mutualistically and antagonistically creating a complex network of species relations to some extent suggesting a co evolutionary network. In this study, I investigate two basic research questions: the first is how plants utilize aposematic and cryptic colours? The second is how animals are affected by the colour signals broadcasted by plants? By using the avian eye model, I discover how visual signals/colours from plants are actually perceived, and the effects of these signals on birds (not human) perception. Aposematism and crypsis are common strategies utilized by animals, yet little evidence is known of such occurrences in plants. Aposematic and cryptic colours were evaluated by studying different colouration strategy through the ontogeny of two native heteroblastic New Zealand plants: Pseudopanax crassifolius and Elaeocarpus hookerianus. To determine the potential effect of colour signals on animals, I investigated an evolutionary theory of leaf colours constraining the conspicuousness of their fruit colour counterparts. Based on the available data, I also conducted a community level analysis about the effects of fruit colours and specific avian frugivores that might be attracted to them. Finally, I examined the fruit colour selection by a frugivorous seed dispersing insect; the Wellington Tree Weta (Hemideina crassidens). My result shows that aposematic and cryptic colours are successfully applied by plants to either warn or remain inconspicuous from browsing herbivores. The evidence I presented lends support to the Moa browsing hypothesis in relation to constraining the conspicuousness of their fruit colour counterparts. Based on the cryptic plant colourations. However, the same level of selective interaction could not be inferred for frugivore fruit colour selection based on avian vision. I demonstrated that leaf reflectance does not constrain/influence the conspicuousness of fruit colours. There was also no fruit colour diversity based on geographical location. Fruit colour alone is not sufficient to influence a specific frugivore assemblage. Other environmental factors and species interaction must be taken into account. Weta proved to possess colour vision capable of colour perception even in low light conditions. Weta also consistently selected naturally blue streaked and manipulated blue coloured fruits of Coprosma acerosa in a binary test. This supports the idea of weta co- evolving with fruit colours of certain divaricating plants in New Zealand. I suggest that the fruit colours of New Zealand are shaped by the combined selection pressure from birds, lizards/geckos and weta.</p>

Visual Signalling in Plant-Animal Interactions

<p>The process of visual signalling between plant and animals is often a combination of exciting discoveries and more often than not; highly controversial hypotheses. Plants and animals interact mutualistically and antagonistically creating a complex network of species relations to some extent suggesting a co evolutionary network. In this study, I investigate two basic research questions: the first is how plants utilize aposematic and cryptic colours? The second is how animals are affected by the colour signals broadcasted by plants? By using the avian eye model, I discover how visual signals/colours from plants are actually perceived, and the effects of these signals on birds (not human) perception. Aposematism and crypsis are common strategies utilized by animals, yet little evidence is known of such occurrences in plants. Aposematic and cryptic colours were evaluated by studying different colouration strategy through the ontogeny of two native heteroblastic New Zealand plants: Pseudopanax crassifolius and Elaeocarpus hookerianus. To determine the potential effect of colour signals on animals, I investigated an evolutionary theory of leaf colours constraining the conspicuousness of their fruit colour counterparts. Based on the available data, I also conducted a community level analysis about the effects of fruit colours and specific avian frugivores that might be attracted to them. Finally, I examined the fruit colour selection by a frugivorous seed dispersing insect; the Wellington Tree Weta (Hemideina crassidens). My result shows that aposematic and cryptic colours are successfully applied by plants to either warn or remain inconspicuous from browsing herbivores. The evidence I presented lends support to the Moa browsing hypothesis in relation to constraining the conspicuousness of their fruit colour counterparts. Based on the cryptic plant colourations. However, the same level of selective interaction could not be inferred for frugivore fruit colour selection based on avian vision. I demonstrated that leaf reflectance does not constrain/influence the conspicuousness of fruit colours. There was also no fruit colour diversity based on geographical location. Fruit colour alone is not sufficient to influence a specific frugivore assemblage. Other environmental factors and species interaction must be taken into account. Weta proved to possess colour vision capable of colour perception even in low light conditions. Weta also consistently selected naturally blue streaked and manipulated blue coloured fruits of Coprosma acerosa in a binary test. This supports the idea of weta co- evolving with fruit colours of certain divaricating plants in New Zealand. I suggest that the fruit colours of New Zealand are shaped by the combined selection pressure from birds, lizards/geckos and weta.</p>

Motion: enhancing signals and concealing cues

ABSTRACT Animal colour patterns remain a lively focus of evolutionary and behavioural ecology, despite the considerable conceptual and technical developments over the last four decades. Nevertheless, our current understanding of the function and efficacy of animal colour patterns remains largely shaped by a focus on stationary animals, typically in a static background. Yet, this rarely reflects the natural world: most animals are mobile in their search for food and mates, and their surrounding environment is usually dynamic. Thus, visual signalling involves not only animal colour patterns, but also the patterns of animal motion and behaviour, often in the context of a potentially dynamic background. While motion can reveal information about the signaller by attracting attention or revealing signaller attributes, motion can also be a means of concealing cues, by reducing the likelihood of detection (motion camouflage, motion masquerade and flicker-fusion effect) or the likelihood of capture following detection (motion dazzle and confusion effect). The interaction between the colour patterns of the animal and its local environment is further affected by the behaviour of the individual. Our review details how motion is intricately linked to signalling and suggests some avenues for future research. This Review has an associated Future Leader to Watch interview with the first author.

Acoustic and visual adaptations to predation risk: A predator affects communication in vocal female fish

Predation is an important ecological constraint that influences communication in animals. Fish respond to predators by adjusting their visual signalling behaviour, but the responses in calling behaviour in the presence of a visually detected predator are largely unknown. We hypothesize that fish will reduce visual and acoustic signalling including sound levels and avoid escalating fights in the presence of a predator. To test this we investigated dyadic contests in female croaking gouramis (Trichopsis vittata, Osphronemidae) in the presence and absence of a predator (Astronotus ocellatus, Cichlidae) in an adjoining tank. Agonistic behaviour in T. vittata consists of lateral (visual) displays, antiparallel circling and production of croaking sounds and may escalate to frontal displays. We analysed the number and duration of lateral display bouts, the number, duration, sound pressure level and dominant frequency of croaking sounds as well as contest outcomes. The number and duration of lateral displays decreased significantly in predator as compared to no-predator trials. Total number of sounds per contest dropped in parallel but no significant changes were observed in sound characteristics. In the presence of a predator dyadic contests were decided or terminated during lateral displays and never escalated to frontal displays. The gouramis showed approaching behaviour towards the predator between lateral displays. This is the first study supporting the hypothesis that predators reduce visual and acoustic signalling in a vocal fish. Sound properties, in contrast, did not change. Decreased signalling and the lack of escalating contests reduce the fish’s conspicuousness and thus predation threat.

Visual marking in mammals first proved by manipulations of brown bear tree debarking

The rather limited human ability to understand animal vision and visual signalling has frequently clouded our expectations concerning the visual abilities of other animals. But there are multiple reasons to suspect that visual signalling is more widely employed by animals than previously thought. Because visibility of visual marks depends on the background in which they are seen, species spending most of their time living in dark conditions (e.g., in forests and/or having crepuscular and nocturnal habits) may rely on bright signals to enhance visual display. Here, as a result of experimental manipulations, we present, for the first time ever, evidence supporting the use of a new channel of intraspecific communication by a mammal species, i.e., brown bear Ursus arctos adult males relying on visual marks during mating. Bear reactions to our manipulation suggest that visual signalling could represent a widely overlooked mechanism in mammal communication, which may be more broadly employed than was previously thought.

Nocturnal visual displays and call description of the cascade specialist glassfrog Sachatamia orejuela

Although most male frogs call to attract females, vocalizations alone can be ineffective long-range signals in certain environments. To increase conspicuousness and counter the background noise generated by rushing water, a few frog species around the world have evolved visual communication modalities in addition to advertisement calls. These species belong to different families on different continents: a clear example of behavioural convergent evolution. Until now, long-distance visual signalling has not been recorded for any species in the glassfrog family (Centrolenidae). Sachatamia orejuela, an exceptionally camouflaged glassfrog species found within the spray zone of waterfalls, has remained poorly studied. Here, we document its advertisement call for the first time — the frequency of which is higher than perhaps any other glassfrog species, likely an evolutionary response to its disruptive acoustic space — as well as a sequence of non-antagonistic visual signals (foot-flagging, hand-waving, and head-bobbing) that we observed at night.

Shedding light on dark adaptation

The retina is famous for its ability to operate under a broad range of light intensities. This is partly due to the presence of two types of photoreceptor cells, rods and cones. Rods are used mostly for dim light vision, and cones are used for bright light and colour vision. These cells are also able to adapt to a broad range of light intensities using light- and dark-adaptation mechanisms. Dark adaptation is used by the vertebrate retina to increase its visual sensitivity when moving from a brightly lit environment to a dark environment. The brighter the surrounding light, the longer it takes for the retina to adapt to the dark. Most retina biologists have studied dark adaptation by exposing animals to a 90% bleach, meaning that 90% of the light-sensing proteins in these photoreceptor cells have been activated, followed by transfer of these animals to a dark room and analysis of their light sensitivity using electrophysiological methods. In this report, we introduce the basic elements of the visual system and describe how the system might operate during dark adaptation. We also introduce a novel role for cAMP-mediated phosphorylation of G protein-coupled receptor kinase 1 (GRK1), a major kinase in visual signalling.

Multimodality and the origin of a novel communication system in face-to-face interaction

Face-to-face communication is multimodal at its core: it consists of a combination of vocal and visual signalling. However, current evidence suggests that, in the absence of an established communication system, visual signalling, especially in the form of visible gesture, is a more powerful form of communication than vocalization and therefore likely to have played a primary role in the emergence of human language. This argument is based on experimental evidence of how vocal and visual modalities (i.e. gesture) are employed to communicate about familiar concepts when participants cannot use their existing languages. To investigate this further, we introduce an experiment where pairs of participants performed a referential communication task in which they described unfamiliar stimuli in order to reduce reliance on conventional signals. Visual and auditory stimuli were described in three conditions: using visible gestures only, using non-linguistic vocalizations only and given the option to use both (multimodal communication). The results suggest that even in the absence of conventional signals, gesture is a more powerful mode of communication compared with vocalization, but that there are also advantages to multimodality compared to using gesture alone. Participants with an option to produce multimodal signals had comparable accuracy to those using only gesture, but gained an efficiency advantage. The analysis of the interactions between participants showed that interactants developed novel communication systems for unfamiliar stimuli by deploying different modalities flexibly to suit their needs and by taking advantage of multimodality when required.

Body coloration and mechanisms of colour production in Archelosauria: the case of deirocheline turtles

Animal body coloration is a complex trait resulting from the interplay of multiple mechanisms. While many studies address the functions of animal coloration, the mechanisms of colour production still remain unknown in most taxa. Here we compare reflectance spectra, cellular, ultra- and nano-structure of colour-producing elements, and pigment types in two freshwater turtles with contrasting courtship behaviour, Trachemys scripta and Pseudemys concinna . The two species differ in the distribution of pigment cell-types and in pigment diversity. We found xanthophores, melanocytes, abundant iridophores and dermal collagen fibres in stripes of both species. The yellow chin and forelimb stripes of both P. concinna and T. scripta contain xanthophores and iridophores, but the post-orbital regions of the two species differ in cell-type distribution. The yellow post-orbital region of P. concinna contains both xanthophores and iridophores, while T. scripta has only xanthophores in the yellow-red postorbital/zygomatic regions. Moreover, in both species, the xanthophores colouring the yellow-red skin contain carotenoids, pterins and riboflavin, but T. scripta has a higher diversity of pigments than P. concinna . Trachemys s. elegans is sexually dichromatic. Differences in the distribution of pigment cell types across body regions in the two species may be related to visual signalling but do not match predictions based on courtship position. Our results demonstrate that archelosaurs share some colour production mechanisms with amphibians and lepidosaurs (i.e. vertical layering/stacking of different pigment cell types and interplay of carotenoids and pterins), but also employ novel mechanisms (i.e. nano-organization of dermal collagen) shared with mammals.

Body coloration and mechanisms of colour production in Archelosauria: The case of deirocheline turtles

Animal body coloration is a complex trait resulting from the interplay of multiple colour-producing mechanisms. Increasing knowledge of the functional role of animal coloration stresses the need to study the proximate causes of colour production. Here we present a description of colour and colour producing mechanisms in two non-avian archelosaurs, the freshwater turtles Trachemys scripta and Pseudemys concinna. We compare reflectance spectra; cellular, ultra-, and nano-structure of colour-producing elements; and carotenoid/pteridine derivatives contents in the two species. In addition to xanthophores and melanocytes, we found abundant iridophores which may play a role in integumental colour production. We also found abundant dermal collagen fibres that may serve as thermoprotection but possibly also play role in colour production. The colour of yellow-red skin patches results from an interplay between carotenoids and pteridine derivatives. The two species differ in the distribution of pigment cell types along the dorsoventral head axis, as well as in the diversity of pigments involved in colour production, which may be related to visual signalling. Our results indicate that archelosaurs share some colour production mechanisms with amphibians and lepidosaurs, but also employ novel mechanisms based on the nano-organization of the extracellular protein matrix that they share with mammals.