Upper beak depression instead of elevation dominates cranial kinesis in woodpeckers.

The value of birds' ability to move the upper beak relative to the braincase has been shown in vital tasks like feeding and singing. In woodpeckers, such cranial kinesis has been thought to hinder pecking as delivering forceful blows calls for a head functioning as a rigid unit. Here, we tested whether cranial kinesis is constrained in woodpeckers by comparing upper beak rotation during their daily activities such as food handling, calling and gaping with those from closely related species that also have a largely insectivorous diet but do not peck at wood. Both woodpeckers and non-woodpecker insectivores displayed upper beak rotations of up to 8 degrees. However, the direction of upper beak rotation differed significantly between the two groups, with woodpeckers displaying primarily depressions and non-woodpeckers displaying elevations. The divergent upper beak rotation of woodpeckers may be caused either by anatomical modifications to the craniofacial hinge that reduce elevation, by the caudal orientation of the mandible depressor muscle forcing beak depressions, or by both. Our results suggest that pecking does not result in plain rigidification at the upper beak's basis of woodpeckers, but it nevertheless significantly influences the way cranial kinesis is manifested.

Protein-lipid Association in Lizard Chemical Signals.

Chemical communication in terrestrial vertebrates is often built on complex blends, where semiochemical and structural compounds may form an integrated functional unit. In lizards, many species have specialized epidermal glands whose secretions are waxy, homogeneous blends of lipids and proteins, both active in communication. The intimate co-occurrence of such compounds allows us to hypothesize that they should undergo a certain degree of covariation, considering both their semiochemical role and the support-to-lipid function hypothesized for the protein fraction. In order to assess the occurrence and level of protein-lipid covariation, we compared the composition and complexity of the two fractions in the femoral gland secretions of 36 lizard species, combining phylogenetically-informed analysis with tandem mass spectrometry. We found the composition and complexity of the two fractions to be strongly correlated. The composition of the protein fraction was mostly influenced by the relative proportion of cholestanol, provitamin D3, stigmasterol, and tocopherol, while the complexity of the protein pattern increased with that of lipids. Additionally, two identified proteins (carbonic anhydrase and protein disulfide isomerase) increased their concentration as provitamin D3 became more abundant. Although our approach does not allow us to decrypt the functional relations between the proteinaceous and lipid components, nor under the semiochemical or structural hypothesis, the finding that the proteins involved in this association were enzymes opens up to new perspectives about protein role: They may confer dynamic properties to the blend, making it able to compensate predictable variation of the environmental conditions. This may expand the view about proteins in the support-to-lipid hypothesis, from being a passive and inert component of the secretions to become an active and dynamic one, thus providing cues for future research.

(Italian) RiassuntoLa comunicazione chimica nei vertebrati terrestri è spesso costituita da miscele complesse, in cui composti semiochimici e strutturali possono formare un"unità funzionale integrata. Nelle lucertole, molte specie hanno ghiandole epidermiche specializzate le cui secrezioni sono miscele cerose e omogenee di lipidi e proteine, entrambe attive nella comunicazione. L"intima coesistenza di tali composti lascia ipotizzare che essi debbano subire un certo grado di co-variazione, sia considerando il loro ruolo semiochimico, sia la funzione di supporto ai lipidi ipotizzata per la frazione proteica. Per valutare la presenza e il livello di covariazione proteine-lipidi, abbiamo confrontato la composizione e la complessità delle due frazioni nelle secrezioni della ghiandola femorale di 36 specie di lucertole, combinando l"analisi filogenetica comparativa con la spettrometria di massa. Abbiamo riscontrato una forte correlazione tra la composizione e la complessità delle due frazioni. La composizione della frazione proteica è stata influenzata soprattutto dalla proporzione relativa di colestanolo, provitamina D3, stigmasterolo e tocoferolo, mentre la complessità del pattern proteico è aumentata con quella dei lipidi. Inoltre, due proteine identificate (anidrasi carbonica e disolfuro isomerasi) hanno aumentato la loro concentrazione al crescere dell'abbondanza della provitamina D3. Sebbene il nostro approccio non consenta di decifrare le relazioni funzionali tra le componenti proteiche e lipidiche, né secondo l"ipotesi semiochimica né secondo quella strutturale, la scoperta che le proteine coinvolte in questa associazione sono enzimi apre a nuove prospettive sul ruolo delle proteine stesse: esse potrebbero conferire proprietà dinamiche alla miscela, rendendola capace di compensare le prevedibili variazioni delle condizioni ambientali. Questo può ampliare la visione delle proteine nell'ipotesi che esse siano di supporto ai lipidi, da componente passiva e inerte delle secrezioni a componente attiva e dinamica, fornendo così spunti per ricerche future.

Climate-related environmental variation in a visual signalling device: the male and female dewlap in Anolis sagrei lizards.

Animals communicate using a variety of signals that differ dramatically among and within species. The astonishing dewlap diversity in anoles has attracted considerable attention in this respect. Yet, the evolutionary processes behind it remain elusive and have mostly been explored for males only. Here, we considered Anolis sagrei males and females to study signal divergence among populations. First, we assessed the degree of variation in dewlap design (size, pattern and colour) and displays by comparing 17 populations distributed across the Caribbean. Second, we assessed whether the observed dewlap diversity is associated with variation in climate-related environmental conditions. Results showed that populations differed in all dewlap characteristics, with the exception of display rate in females. We further found that males and females occurring in 'xeric' environments had a higher proportion of solid dewlaps with higher UV reflectance. In addition, lizards inhabiting 'mesic' environments had primarily marginal dewlaps showing high reflectance in red. For dewlap display, a correlation with environment was only observed in males. Our study provides evidence for a strong relationship between signal design and prevailing environmental conditions, which may result from differential selection on signal efficacy. Moreover, our study highlights the importance of including females when studying dewlaps in an evolutionary context.

How phylogeny and foraging ecology drive the level of chemosensory exploration in lizards and snakes.

The chemical senses are crucial for squamates (lizards and snakes). The extent to which squamates utilize their chemosensory system, however, varies greatly among taxa and species' foraging strategies, and played an influential role in squamate evolution. In lizards, 'Scleroglossa' evolved a state where species use chemical cues to search for food (active foragers), whereas 'Iguania' retained the use of vision to hunt prey (ambush foragers). However, such strict dichotomy is flawed as shifts in foraging modes have occurred in all clades. Here, we attempted to disentangle effects of foraging ecology from phylogenetic trait conservatism as leading cause of the disparity in chemosensory investment among squamates. To do so, we used species' tongue-flick rate (TFR) in the absence of ecological relevant chemical stimuli as a proxy for its fundamental level of chemosensory investigation, that is baseline TFR. Based on literature data of nearly 100 species and using phylogenetic comparative methods, we tested whether and how foraging mode and diet affect baseline TFR. Our results show that baseline TFR is higher in active than ambush foragers. Although baseline TFRs appear phylogenetically stable in some lizard taxa, that is a consequence of concordant stability of foraging mode: when foraging mode shifts within taxa, so does baseline TFR. Also, baseline TFR is a good predictor of prey chemical discriminatory ability, as we established a strong positive relationship between baseline TFR and TFR in response to prey. Baseline TFR is unrelated to diet. Essentially, foraging mode, not phylogenetic relatedness, drives convergent evolution of similar levels of squamate chemosensory investigation.