THERMOREGULATION CONSTRAINS EFFECTIVE WARNING SIGNAL EXPRESSION

Evolution of conspicuous signals may be constrained if animal coloration has nonsignaling as well as signaling functions. In aposematic wood tiger moth ( Parasemia plantaginis ) larvae, the size of a warning signal (orange patch on black body) varies phenotypically and genetically. Although a large warning signal is favored as an antipredator defense, we hypothesized that thermoregulation may constrain the signal size in colder habitats. To test this hypothesis, we conducted a factorial rearing experiment with two selection lines for larval coloration (small and large signal) and with two temperature manipulations (high and low temperature environment). Temperature constrained the size and brightness of the warning signal. Larvae with a small signal had an advantage in the colder environment, which was demonstrated by a faster development time and growth rate in the low temperature treatment, compared to larvae with a large signal. Interestingly, the larvae with a small signal were found more often on the plant than the ones with a large signal, suggesting higher basking activity of the melanic (small signal) individuals in the low temperature. We conclude that the expression of aposematic display is not only defined by its efficacy against predators; variation in temperature may constrain evolution of a conspicuous warning signal and maintain variation in it.     

Experimental evidence for paternal effects on offspring growth rate in Arctic charr (Salvelinus alpinus)

Sexual selection theory predicts that females should choose males that signal viability and quality. However, few studies have found fitness benefits among females mating with highly ornamented males. Here, we use Arctic charr (Salvelinus alpinus), a teleost fish with no parental care, to investigate whether females could gain fitness benefits by mating with highly ornamented and large-sized males. Carotenoid-based coloration signalled by males during spawning is believed to be an indicator of good genes for this species. Paternal effects on offspring size (body length and dry body mass) were examined experimentally by crossing eggs and sperm in vitro from 12 females and 24 males in a split-brood design and raising larvae to 30 days past hatching. We clearly demonstrated that there was a relationship between offspring size and paternal coloration. However, a negative interaction between paternal length and coloration was evident for offspring length, indicating that positive effects of paternal coloration were only present for smaller males. Thus, the red spawning coloration of the male Arctic charr seems to be an indicator of good genes, but the effect of paternal coloration on offspring length, an indicator of 'offspring quality', is size dependent.     

The role of nocturnal vision in mate choice: females prefer conspicuous males in the European tree frog (Hyla arborea)

Nocturnal frog species rely extensively on vocalization for reproduction. But recent studies provide evidence for an important, though long overlooked, role of visual communication. In many species, calling males exhibit a conspicuous pulsing vocal sac, a signal bearing visually important dynamic components. Here, we investigate female preference for male vocal sac coloration—a question hitherto unexplored—and male colour pattern in the European tree frog (Hyla arborea). Under nocturnal conditions, we conducted two-choice experiments involving video playbacks of calling males with identical calls and showing various naturally encountered colour signals, differing in their chromatic and brightness components. We adjusted video colours to match the frogs'' visual perception, a crucial aspect not considered in previous experiments. Females prefer males with a colourful sac and a pronounced flank stripe. Both signals probably enhance male conspicuousness and facilitate detection and localization by females. This study provides the first experimental evidence of a preference for specific vocal sac spectral properties in a nocturnal anuran species. Vocal sac coloration is based on carotenoids and may convey information about male quality worthwhile for females to assess. The informative content of the flank stripe remains to be demonstrated.     

Does colour polymorphism enhance survival of prey populations?

That colour polymorphism may protect prey populations from predation is an old but rarely tested hypothesis. We examine whether colour polymorphic populations of prey exposed to avian predators in an ecologically valid visual context were exposed to increased extinction risk compared with monomorphic populations. We made 2976 artificial pastry prey, resembling Lepidoptera larvae, in four different colours and presented them in 124 monomorphic and 124 tetramorphic populations on tree trunks and branches such that they would be exposed to predation by free-living birds, and monitored their ‘survival’. Among monomorphic populations, there was a significant effect of prey coloration on survival, confirming that coloration influenced susceptibility to visually oriented predators. Survival of polymorphic populations was inferior to that of monomorphic green populations, but did not differ significantly from monomorphic brown, yellow or red populations. Differences in survival within polymorphic populations paralleled those seen among monomorphic populations; the red morph most frequently went extinct first and the green morph most frequently survived the longest. Our findings do not support the traditional protective polymorphism hypothesis and are in conflict with those of earlier studies. As a possible explanation to our findings, we offer a competing ‘giveaway cue’ hypothesis: that polymorphic populations may include one morph that attracts the attention of predators and that polymorphic populations therefore may suffer increased predation compared with some monomorphic populations.     

Manipulation of male attractiveness induces rapid changes in avian maternal yolk androgen deposition

Avian eggs contain maternal androgens that may adjust offspringdevelopment to environmental conditions. We review evidenceand functional explanations for the relationship between androgenconcentrations in avian eggs and male attractiveness. Experimentalstudies in captive birds show generally positive relationships,but results from correlational and experimental field studiesare less consistent, perhaps because they lack a within-femaledesign to control for confounding between-female variation.We analyzed the effect of male attractiveness on yolk levelsof maternal androgens in a wild bird, using a correlationaland experimental approach with a within-female design. We manipulatedthe sexually selected UV coloration of the crown feathers ofmale blue tits (Cyanistes caeruleus) after their female hadlaid the second egg and measured the subsequent effect on androgenconcentrations (testosterone and androstenedione) in the fifth,seventh, and ninth eggs relative to that in the second egg.Levels of testosterone, but not androstenedione, in eggs 5 and7 were higher for control (attractive) than for UV-reduced (unattractive)males. This effect disappeared in the ninth egg, coincidingwith the recovery of UV coloration after manipulation. Thissuggests that females are capable of rapid adjustments of testosteronedeposition in response to changes in their mate's ornamentalplumage. However, androgen concentrations in the second eggand pretreatment male crown coloration were not correlated.Possibly, the combination of relatively small variation in UVcoloration before treatment and the influence of unknown confoundingvariables in the correlative approach resulted in insufficientstatistical power to detect such a correlation.     

Systematic revision of the genus Everettia Godwin‐Austen, 1891 (Mollusca: Gastropoda: Dyakiidae) in Sabah,northern Borneo

The species of the snail genus Everettia in the Malaysian state of Sabah are superficially similar and difficult to distinguish by their shells. This paper presents new data on the taxonomy and distribution of Everettia in Sabah that have accumulated since the revision by Godwin‐Austen in 1891. By using morphological and molecular phylogenetic approaches, we reveal at least seventeen species of Everettia in Sabah, of which eleven are new to science, namely: Everettia layanglayang sp. nov. , Everettia lapidini sp. nov. , Everettia paulbasintali sp. nov. , Everettia occidentalis sp. nov. , Everettia jasilini sp. nov. , Everettia safriei sp. nov. , Everettia interior sp. nov. , Everettia jucundior sp. nov. , Everettia planispira sp. nov. , Everettia monticola sp. nov. , and Everettia dominiki sp. nov. , and one new subspecies, namely, Everettia corrugata williamsi ssp. nov. Phylogenetic analysis of mitochondrial COI and 16S, and nuclear ITS‐1 sequences demonstrates the monophyly of most of the morphologically well‐defined species. Our results show that certain aspects of classical morphology‐based taxonomy for Everettia species, especially with regard to the unique combination of shell surface sculptures, animal head colour, and mantle pigmentation, are solid. A dichotomous key to the Sabah species and subspecies of Everettia is provided. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 157 , 515–550.     

Unripe red fruits may be aposematic

The unripe fruits of certain species are red. Some of these species disperse their seeds by wind (Nerium oleander, Anabasis articulata), others by adhering to animals with their spines (Emex spinosa) or prickles (Hedysarum spinosissimum). Certainly neither type uses red coloration as advertisement to attract the seed dispersing agents. Fleshy-fruited species (Rhamnus alaternus, Rubus sanguineus and Pistacia sp.), which disperse their seeds via frugivores, change fruit color from green to red while still unripe and then to black or dark blue upon ripening. The red color does not seem to function primarily in dispersal (unless red fruits form advertisement flags when there are already black ripe fruits on the plant) because the red unripe fruits of these species are poisonous, spiny, or unpalatable. The unripe red fruits of Nerium oleander are very poisonous, those of Rhamnus alaternus and Anabasis articulata are moderately poisonous, those of Rubus sanguineus are very sour, those of Pistacia sp. contain unpalatable resin and those of Emex spinosa and Hedysarum spinosissimum are prickly. We propose that these unripe red fruits are aposematic, protecting them from herbivory before seed maturation.     

Localization of a flavonoid biosynthetic polyphenol oxidase in vacuoles

Aureusidin synthase, a polyphenol oxidase (PPO), specifically catalyzes the oxidative formation of aurones from chalcones, which are plant flavonoids, and is responsible for the yellow coloration of snapdragon (Antirrhinum majus) flowers. All known PPOs have been found to be localized in plastids, whereas flavonoid biosynthesis is thought to take place in the cytoplasm [or on the cytoplasmic surface of the endoplasmic reticulum (ER)]. However, the primary structural characteristics of aureusidin synthase and some of its molecular properties argue against localization of the enzyme in plastids and the cytoplasm. In this study, the subcellular localization of the enzyme in petal cells of the yellow snapdragon was investigated. Sucrose-density gradient and differential centrifugation analyses suggested that the enzyme (the 39-kDa mature form) is not located in plastids or on the ER. Transient assays using a green fluorescent protein (GFP) chimera fused with the putative propeptide of the PPO precursor suggested that the enzyme was localized within the vacuole lumen. We also found that the necessary information for vacuolar targeting of the PPO was encoded within the 53-residue N-terminal sequence (NTPP), but not in the C-terminal sequence of the precursor. NTPP-mediated ER-to-Golgi trafficking to vacuoles was confirmed by means of the co-expression of an NTPP-GFP chimera with a dominant negative mutant of the Arabidopsis GTPase Sar1 or with a monomeric red fluorescent protein (mRFP)-fused Golgi marker (an H+-translocating inorganic pyrophosphatase of Arabidopsis). We identified a sequence-specific vacuolar sorting determinant in the NTPP of the precursor. We have demonstrated the biosynthesis of a flavonoid skeleton in vacuoles. The findings of this metabolic compartmentation may provide a strategy for overcoming the biochemical instability of the precursor chalcones in the cytoplasm, thus leading to the efficient accumulation of aurones in the flower.