Are viviparous lizards from cool climates ever exclusively nocturnal? Evidence for extensive basking in a New Zealand gecko

Viviparity has evolved numerous times among squamate reptiles; however, the combination of viviparity and nocturnality is apparently rare among lizards. We used time‐lapse photography to examine evidence for diurnal activity in a viviparous lizard often described as nocturnal, the gecko Woodworthia ‘Otago/Southland’ from southern New Zealand (family Diplodactylidae). Evidence for diurnal emergence was extensive. Females have a higher incidence of basking compared to males, although no difference was detected between females in different reproductive conditions. Temperature loggers inserted into calibrated copper models were used to compare the body temperatures available to geckos in two basking positions and in two retreat types. Models in basking positions reached higher mean temperatures than models in retreats, although there was no significant effect of basking position or retreat type on model temperatures. Collectively, our results indicate that pregnant geckos that bask consistently could reduce gestation length by at least 14 days compared with females that remain in retreats. Extensive basking in this species adds to the growing evidence of diurno‐nocturnality in many New Zealand lepidosaurs, including other viviparous geckos. Our results lead us to question whether viviparity in lizards is ever compatible with ‘pure’ nocturnality in a cool climate. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●● , ●●–●●.     

Low cost of locomotion in lizards that are active at low temperatures

The nocturnality hypothesis of K. Autumn and coworkers states that nocturnal geckos have evolved a low energetic cost of locomotion (C(min)). A low C(min) increases maximum aerobic speed and partially offsets the decrease in maximum oxygen consumption caused by activity at low nocturnal temperatures. We tested whether a low C(min) is unique to nocturnal geckos or represents a more general pattern of convergent evolution among lizards that enables nocturnality and/or cold-temperature activity. We measured C(min) in four carefully selected lizard species from New Zealand (two nocturnal and two diurnal; n=5-9 individuals per species), including a nocturnal and diurnal gecko (a low C(min) is a gecko trait and is not related to nocturnality), a nocturnal skink (a low C(min) is related to being nocturnal), and a diurnal skink active at low temperatures (a low C(min) is related to being active at low body temperatures). The C(min) values of the four species measured in this study (range=0.21-2.00 mL O(2) g(-1) km(-1)) are lower than those of diurnal lizards from elsewhere, and the values are within or below the 95% confidence limits previously published for nocturnal geckos. A low C(min) increases the range of locomotor speeds possible at low temperatures and provides an advantage for lizards active at these temperatures. We accepted the hypothesis that nocturnal lizards in general have a low C(min) and provide evidence for a low C(min) in lizards from cool-temperate environments. The low C(min) in lizards living at high latitudes may enable extension of their latitudinal range into otherwise thermally suboptimal habitats.     

Secondarily diurnal geckos return to cost of locomotion typical of diurnal lizards

Previous studies showed that nocturnal geckos evolved a low energetic cost of locomotion (Cmin), which increases maximum aerobic speed and partially offsets the decrease in maximal oxygen consumption caused by activity at low nocturnal temperatures. Because the advantage of a low Cmin should apply at high diurnal temperatures as well as at low nocturnal temperatures, I hypothesized that Cmin remained low in geckos that have secondarily evolved diurnality. I measured Cmin in two secondarily diurnal gecko species, Rhoptropus bradfieldi (4.7 g+/-0.71 SE) and Phelsuma madagascariensis (23.9 g+/-3.7 SE), during steady exercise on a treadmill and rejected the hypothesis that secondarily diurnal geckos retain the low Cmin of their nocturnal ancestors. The Cmin in R. bradfieldi (2.468 mL O2 g-1 km-1+/-0.489 SE) and P. madagascariensis (1.389 mL O2 g-1 km-1+/-0.119 SE) returned to values typical of ancestrally diurnal lizards. This suggests that there is a trade-off that outweighs the performance advantage of low Cmin in a diurnal environment and that may cause an evolutionary association between Cmin and activity time (diurnality/nocturnality).     

Gecko vision—visual cells,evolution, and ecological constraints

Geckos comprise both nocturnal and diurnal genera, and between these categories there are several transitions. As all geckos depend on their visual sense for prey capture, they are promising subjects for comparison of morphological modifications of visual cells adapted to very different photic environments. Retinae of 22 species belonging to 15 genera with different activity periods are examined electron microscopically. Scotopic and photopic vision in geckos is not divided between “classical” rods and cones, respectively; both are performed by one basic visual cell type. Independent of the activity periods of the individual species, the visual cells of geckos exhibit characteristics of cones at all levels of their ultrastructure. Thus, gecko retinae have to be classified as cone retinae. Only the large size and the shape of the photoreceptor outer segments in nocturnal geckos are reminiscent of rods; the outer segments are up to 60 μm in length and up to 10 μm in diameter. The visual cells of diurnal geckos have considerably smaller outer segments with lengths ranging from 6 to 12 μm and diameters ranging from 1.3 to 2.1 μm. Nocturnal and diurnal species differ in the structure of their ellipsoids. One type of visual cell in nocturnal geckos has modified mitochondria with either rudimentary cristae or no cristae at all, and one type of visual cell in diurnal geckos possesses an oil droplet. The visual cells of Phelsuma guentheri and Rhoptropus barnardi are intermediate between those of nocturnal and diurnal species.     

Total lactate dehydrogenase activity of tail muscle is not cold-adapted in nocturnal lizards from cool-temperate habitats

The dependence of metabolic processes on temperature constrains the behavior, physiology and ecology of many ectothermic animals. The evolution of nocturnality in lizards, especially in temperate regions, requires adaptations for activity at low temperatures when optimal body temperatures are unlikely to be obtained. We examined whether nocturnal lizards have cold-adapted lactate dehydrogenase (LDH). LDH was chosen as a representative metabolic enzyme. We measured LDH activity of tail muscle in six lizard species (n = 123: three nocturnal, two diurnal and one crepuscular) between 5 and 35 °C and found no differences in LDH-specific activity or thermal sensitivity among the species. Similarly, the specific activity and thermal sensitivity of LDH were similar between skinks and geckos. Similar enzyme activities among nocturnal and diurnal lizards indicate that there is no selection of temperature specific LDH enzyme activity at any temperature. As many nocturnal lizards actively thermoregulate during the day, LDH may be adapted for a broad range of temperatures rather than adapted specifically for the low temperatures encountered when the animals are active. The total activity of LDH in tropical and temperate lizards is not cold-adapted. More data are required on biochemical adaptations and whole animal thermal preferences before trends can be established.     

Evolution of visual pigments in geckos

Most geckos are nocturnal forms and possess rod retinas, but some diurnal genera have pure-cone retinas. We isolated cDNAs encoding the diurnal gecko opsins, dg1 and dg2, similar to nocturnal gecko P521 and P467, respectively. Despite the large morphological differences between the diurnal and nocturnal gecko photoreceptor types, they express phylogenetically closely related opsins. These results provide molecular evidence for the reverse transmutation, that is, rods of an ancestral nocturnal gecko have backed into cones of diurnal geckos. The amino acid substitution rates of dgl and dg2 are higher than those of P521 and P467, respectively. Changes of behavior regarding photic environment may have contributed to acceleration of amino acid substitutions in the diurnal gecko opsins.     

LOCOMOTOR PERFORMANCE AT LOW TEMPERATURE AND THE EVOLUTION OF NOCTURNALITY IN GECKOS

Nocturnal geckos are active at body temperatures 10–35°C below the thermal optima for maximum rate of aerobic metabolism of diurnal lizards. Therefore, given ancestral (diurnal) lizard physiology, nocturnality causes a substantial thermal handicap in locomotor performance. In prior studies, we hypothesized that a low minimum cost of locomotion (C_min) in geckos was an adaptation that increased locomotor endurance capacity at low, nocturnal temperatures. However, C_min is only part of an integrated system that, in conjunction with the maximum rate of oxygen consumption, sets the maximum speed that can be sustained aerobically (termed the maximum aerobic speed or MAS). We conducted the first phylogenetic analysis of MAS and lizards and found that the greatest changes in MAS, C_min and (at activity temperatures) in the evolutionary history of lizards all coincided with the evolution of nocturnality in geckos. Geckos active at 15–25°C did not become optimized for nocturnal temperatures, or fully offset the thermal effects of nocturnality by evolving maximal rates of oxygen consumption comparable to diurnal lizards active at 35°C. Geckos did evolve MAS twice that of diurnal lizards running at low temperatures by evolving a remarkably low C_min. Allometric analysis and phylogenetically independent contrasts of , C_min, and MAS indicate a 72% evolutionary decrease in , (at activity temperatures) and a 50% evolutionary decrease in C_min concordant with the evolution of nocturnality in geckos. Experimental measurements show that decreased C_min in six species of gecko increased MAS by 50–120% compared to diurnal lizards at low temperatures. Thus, geckos sufficiently overcame the near paralyzing effects of nocturnal temperatures, but only offset about 50% of the decrease in MAS resulting from the low maximum rate of oxygen consumption. Although the nocturnal environment remains severely suboptimal, the evolution of a low cost of locomotion in the ancestor of geckos was highly adaptive for nocturnality. We also present a generalized approach to ecophysiological evolution that integrates phylogeny with the causal relationships among environment, physiology, and performance capacity. With respect to a clade, two hypotheses are central to our integrative approach: (1) a change of an environmental variable (e.g., temperature) causes a performance handicap; and (2) evolution of a physiological variable (e.g., minimum cost of locomotion [C_min]) increases performance in the derived environment. To test the hypothesis that evolution of a physiological variable is adaptive in nature, we suggest determining if individuals in nature perform at levels exceeding the performance capacity of their hypothetical ancestors and if this additional performance capacity is due to the evolution of the physiological variable in question.     

Environmentally-induced shifts in behavior intensify indirect competition by an invasive gecko in Mauritius

Most recorded extinctions have occurred on oceanic islands, mainly as a result of introduced mammalian predators. The impact of introduced non-mammalian competitors, however, is poorly understood. The house gecko, Hemidactylus frenatus, is one of the most successful invasive reptiles and has been implicated in the decline of endemic geckos and other taxa on a number of tropical and subtropical islands. We investigated the patterns of niche utilization between the house gecko and endemic ornate day gecko, Phelsuma ornata, in Mauritius, two species which were not believed to compete because they had different diel activity periods. The dietary and temporal niche partitioning of the two species were examined in relation to seasonal invertebrate prey abundance for three seasons. Dietary overlap between the two species was least when prey abundance was lowest and temporal overlap in activity greatest. Exploitative competition was therefore inferred, whereby changes in dietary overlap were attributed to shifts in prey selection by the day, but not the house, gecko, which was hypothesized to deplete prey. The compensatory response of the day gecko may have been to increase its tendency for cannibalism, such that the smaller house gecko was indirectly responsible for population reduction of its larger competitor. This is the first study to show how an invasive nocturnal gecko may be affecting a predominantly diurnal species.     

Visual ecology of Indian carpenter bees I: Light intensities and flight activity

Bees are mostly active during the daytime, but nocturnality has been reported in some bee families. We studied temporal flight activity in three species of carpenter bees (genus Xylocopa) in relation to light intensities. X. leucothorax is diurnal, X. tenuiscapa is largely diurnal being only occasionally crepuscular, while X. tranquebarica is truly nocturnal. Occasional forays into dim light by X. tenuiscapa are likely to be due to the availability of richly rewarding Heterophragma quadriloculare (Bignoniaceae) flowers, which open at night. X. tranquebarica can fly even during the moonless parts of nights when light intensities were lower than 10⁻⁵ cd m⁻², which makes this species the only truly nocturnal bee known so far. Other known dim-light species fly during crepuscular or moonlit periods. We compare eye and body sizes with other known diurnal and dim-light bees. We conclude that while extremely large ocellar diameters, large eye size:body size ratio, large number of ommatidia and large ommatidial diameters are all adaptations to dim-light foraging, these alone do not sufficiently explain the flights of X. tranquebarica in extremely dim light. We hypothesise that additional adaptations must confer extreme nocturnality in X. tranquebarica.     

Moonstruck Primates: Owl Monkeys (Aotus) Need Moonlight for Nocturnal Activity in Their Natural Environment

Primates show activity patterns ranging from nocturnality to diurnality, with a few species showing activity both during day and night. Among anthropoids (monkeys, apes and humans), nocturnality is only present in the Central and South American owl monkey genus Aotus. Unlike other tropical Aotus species, the Azara''s owl monkeys (A. azarai) of the subtropics have switched their activity pattern from strict nocturnality to one that also includes regular diurnal activity. Harsher climate, food availability, and the lack of predators or diurnal competitors, have all been proposed as factors favoring evolutionary switches in primate activity patterns. However, the observational nature of most field studies has limited an understanding of the mechanisms responsible for this switch in activity patterns. The goal of our study was to evaluate the hypothesis that masking, namely the stimulatory and/or inhibitory/disinhibitory effects of environmental factors on synchronized circadian locomotor activity, is a key determinant of the unusual activity pattern of Azara''s owl monkeys. We use continuous long-term (6–18 months) 5-min-binned activity records obtained with actimeter collars fitted to wild owl monkeys (n = 10 individuals) to show that this different pattern results from strong masking of activity by the inhibiting and enhancing effects of ambient luminance and temperature. Conclusive evidence for the direct masking effect of light is provided by data showing that locomotor activity was almost completely inhibited when moonlight was shadowed during three lunar eclipses. Temperature also negatively masked locomotor activity, and this masking was manifested even under optimal light conditions. Our results highlight the importance of the masking of circadian rhythmicity as a determinant of nocturnality in wild owl monkeys and suggest that the stimulatory effects of dim light in nocturnal primates may have been selected as an adaptive response to moonlight. Furthermore, our data indicate that changes in sensitivity to specific environmental stimuli may have been an essential key for evolutionary switches between diurnal and nocturnal habits in primates.     

The relationship between the golden spiny mouse circadian system and its diurnal activity: an experimental field enclosures and laboratory study

Examples of animals that switch activity times between nocturnality and diurnality in nature are relatively infrequent. Furthermore, the mechanism for switching activity time is not clear: does a complete inversion of the circadian system occur in conjunction with activity pattern? Are there switching centers downstream from the internal clock that interpret the clock differently? Or does the switch reflect a masking effect? Answering these key questions may shed light on the mechanisms regulating activity patterns and their evolution. The golden spiny mouse (Acomys russatus) can switch between nocturnal and diurnal activity. This study investigated the relationship between its internal circadian clock and its diurnal activity pattern observed in the field. The goal is to understand the mechanisms underlying species rhythm shifts in order to gain insight into the evolution of activity patterns. All golden spiny mice had opposite activity patterns in the field than those under controlled continuous dark conditions in the laboratory. Activity and body temperature patterns in the field were diurnal, while in the laboratory all individuals immediately showed a free-running rhythm starting with a nocturnal pattern. No phase transients were found toward the preferred nocturnal activity pattern, as would be expected in the case of true entrainment. Moreover, the fact that the free-running activity patterns began from the individuals' subjective night suggests that golden spiny mice are nocturnal and that their diurnality in their natural habitat in the field results from a change that is downstream to the internal clock or reflects a masking effect.     

The Relationship between the Golden Spiny Mouse Circadian System and Its Diurnal Activity: An Experimental Field Enclosures and Laboratory Study

Examples of animals that switch activity times between nocturnality and diurnality in nature are relatively infrequent. Furthermore, the mechanism for switching activity time is not clear: does a complete inversion of the circadian system occur in conjunction with activity pattern? Are there switching centers downstream from the internal clock that interpret the clock differently? Or does the switch reflect a masking effect? Answering these key questions may shed light on the mechanisms regulating activity patterns and their evolution. The golden spiny mouse (Acomys russatus) can switch between nocturnal and diurnal activity. This study investigated the relationship between its internal circadian clock and its diurnal activity pattern observed in the field. The goal is to understand the mechanisms underlying species rhythm shifts in order to gain insight into the evolution of activity patterns. All golden spiny mice had opposite activity patterns in the field than those under controlled continuous dark conditions in the laboratory. Activity and body temperature patterns in the field were diurnal, while in the laboratory all individuals immediately showed a free‐running rhythm starting with a nocturnal pattern. No phase transients were found toward the preferred nocturnal activity pattern, as would be expected in the case of true entrainment. Moreover, the fact that the free‐running activity patterns began from the individuals' subjective night suggests that golden spiny mice are nocturnal and that their diurnality in their natural habitat in the field results from a change that is downstream to the internal clock or reflects a masking effect.     

Evolution of activity patterns and chromatic vision in primates: morphometrics, genetics and cladistics

Hypotheses for the adaptive origin of primates have reconstructed nocturnality as the primitive activity pattern for the entire order based on functional/adaptive interpretations of the relative size and orientation of the orbits, body size and dietary reconstruction. Based on comparative data from extant taxa this reconstruction implies that basal primates were also solitary, faunivorous, and arboreal. Recently, primates have been hypothesized to be primitively diurnal, based in part on the distribution of color-sensitive photoreceptor opsin genes and active trichromatic color vision in several extant strepsirrhines, as well as anthropoid primates (Tan & Li, 1999 Nature402, 36; Li, 2000 Am. J. phys. Anthrop. Supple.30, 318). If diurnality is primitive for all primates then the functional and adaptive significance of aspects of strepsirrhine retinal morphology and other adaptations of the primate visual system such as high acuity stereopsis, have been misinterpreted for decades. This hypothesis also implies that nocturnality evolved numerous times in primates. However, the hypothesis that primates are primitively diurnal has not been analyzed in a phylogenetic context, nor have the activity patterns of several fossil primates been considered.This study investigated the evolution of activity patterns and trichromacy in primates using a new method for reconstructing activity patterns in fragmentary fossils and by reconstructing visual system character evolution at key ancestral nodes of primate higher taxa. Results support previous studies that reconstruct omomyiform primates as nocturnal. The larger body sizes of adapiform primates confound inferences regarding activity pattern evolution in this group. The hypothesis of diurnality and trichromacy as primitive for primates is not supported by the phylogenetic data. On the contrary, nocturnality and dichromatic vision are not only primitive for all primates, but also for extant strepsirrhines. Diurnality, and possibly X-linked polymorphic trichromacy, evolved at least in the stem lineage of Anthropoidea, or the stem lineage of all haplorhines.     

Nesting in a thermally challenging environment: nest‐site selection in a rock‐dwelling gecko,Oedura lesueurii (Reptilia: Gekkonidae)

In egg‐laying species, maternal oviposition choice can influence egg survival and offspring phenotypes. According to the maternal‐preference offspring‐performance hypothesis, females should choose oviposition sites that are optimal for offspring fitness. However, in thermally challenging environments, maternal oviposition behaviour may be constrained by the limited availability of suitable oviposition sites. We investigated nest‐site selection in a nocturnal lizard [velvet gecko Oedura lesueurii (Duméril and Bibron)] that inhabits a thermally challenging environment in south‐eastern Australia. The viability of these gecko populations is critical for the persistence of an endangered snake species (Hoplocephalus bungaroides Wagler) that feeds heavily on velvet geckos. Female geckos chose nest sites nonrandomly, with 87% of nests (N = 30) being laid in deep crevices. By contrast, only 13% of clutches were laid under rocks, which were the most readily available potential nest sites. Nest success in crevices was high (100%), but no eggs hatched from nests under rocks. Temperatures in nest crevices remained relatively low and constant throughout the incubation period (mean = 22.7 °C, range 21.0–24.5 °C), whereas thermal regimes under rocks showed large diurnal fluctuations. Geckos selected crevices that were deeper, had less canopy cover, and were warmer than most available crevices; in 85% of cases, such crevices were used simultaneously by more than one female. The thermally distinctive attributes of nest sites, and their frequent communal use, suggest that nest sites are a scarce resource for female velvet geckos, and that the shading of rock outcrops through vegetation encroachment may influence nest success in this species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 250–259.     

Gobekko cretacicus (Reptilia: Squamata) and its bearing on the interpretation of gekkotan affinities

Gobekko cretacicus, a Cretaceous lizard from the Gobi Desert of Mongolia, is a key fossil for understanding gecko phylogeny. We revisit this fossil using high‐resolution X‐ray computed tomography. The application of this imaging method reveals new information about sutures, bone shape, and structural details of the palate and basicranium. These data were used to assess the phylogenetic affinities of Gobekko in the context of an existing squamate data set. The effects of character ordering, search strategy, and the addition of another putative gekkonomorph (Hoburogekko suchanovi) on inferred gekkonomorph relationships were explored. Available specimens of G. cretacicus are skeletally mature but have unfused nasals, frontals, and parietals, and (possibly) a persistent basicranial fenestra. Some putative gekkonomorphs are not consistently supported as closer to crown clade gekkotans than to autarchoglossans. In a strict consensus both Gobekko and Hoburogekko form a polytomy with extant geckos. Some of the adult character states of Gobekko are observable in embryos of extant species. The evolution of tubular frontals and dentaries in gekkotans may be structurally related to the loss of the postorbital and supratemporal bars in this lineage. The complete lack of a parietal foramen, and presumably a light‐sensitive parietal eye, in this clade is of interest and could indicate an early origin of nocturnality in geckos. © 2013 The Linnean Society of London     

Diel behavior in moths and butterflies: a synthesis of data illuminates the evolution of temporal activity

Lepidoptera (butterflies and moths) are one of the most taxonomically diverse insect orders with nearly 160,000 described species. They have been studied extensively for centuries and are found on nearly all continents and in many environments. It is often assumed that adult butterflies are strictly diurnal and adult moths are strictly nocturnal, but there are many exceptions. Despite the broad interest in butterflies and moths, a comprehensive review of diel (day-night) activity has not been conducted. Here, we synthesize existing data on diel activity in Lepidoptera, trace its evolutionary history on a phylogeny, and show where gaps lie in our knowledge. Diurnality was likely the ancestral condition in Lepidoptera, the ancestral heteroneuran was likely nocturnal, and more than 40 transitions to diurnality subsequently occurred. Using species diversity estimates across the order, we predict that roughly 75-85% of Lepidoptera are nocturnal. We also define the three frequently used terms for activity in animals (diurnal, nocturnal, crepuscular), and show that literature on the activity of micro-moths is significantly lacking. Ecological factors leading to nocturnality/diurnality is a compelling area of research and should be the focus of future studies.     

Length–mass allometry in snakes

Body size and body shape are tightly related to an animal's physiology, ecology and life history, and, as such, play a major role in understanding ecological and evolutionary phenomena. Because organisms have different shapes, only a uniform proxy of size, such as mass, may be suitable for comparisons between taxa. Unfortunately, snake masses are rarely reported in the literature. On the basis of 423 species of snakes in 10 families, we developed clade‐specific equations for the estimation of snake masses from snout–vent lengths and total lengths. We found that snout–vent lengths predict masses better than total lengths. By examining the effects of phylogeny, as well as ecological and life history traits on the relationship between mass and length, we found that viviparous species are heavier than oviparous species, and diurnal species are heavier than nocturnal species. Furthermore, microhabitat preferences profoundly influence body shape: arboreal snakes are lighter than terrestrial snakes, whereas aquatic snakes are heavier than terrestrial snakes of a similar length. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Different environments lead to a reversal in the expression of weapons and testes in the heliconia bug,Leptoscelis tricolor (Hemiptera: Coreidae)

In many species, males invest both in weapons used in competitions for access to mates and testes size to increase competitive chances for fertilizations. The expression of weapons and testes can be sensitive to environmental factors experienced during development. However, relatively few studies have examined the effects of discrete, natural developmental environments on the expression of these traits in wild populations. In the present study, we examined the development of these primary and secondary sexual traits for the Heliconia bug, Leptoscelis tricolor (Hemiptera: Coreidae) across two different natural host plants, Heliconia mariae and Heliconia platystachys. Development on H. platystachys resulted in increased investment in weapons and reduced investment in testes, whereas development on H. mariae resulted in the opposite pattern. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●● , ●●–●●.     

The evolution of symmetrical snapping in termite soldiers need not lead to reduced chemical defence

Termite soldiers use a multitude of defensive strategies, often combining mechanical weapons with defensive chemicals secreted from their frontal gland. In higher termites (Termitidae), both these weapons are situated in the head of the soldiers. Their simultaneous occurrence is supposed to be subjected to energetic and spatial constraints and the resulting trade‐off often leads to a full development of only one of the weapons and reduction of the other. Mandibular snapping represents an extreme and efficient anatomical adaptation, allowing the soldier to knock out arthropod enemies with a violent strike of elongated mandibles. The head of snapping soldiers harbours massive adductor muscles while the frontal gland is reported to be reduced and the chemical defence absent. Here we show that the symmetrical snapping soldiers of the Neotropical termite Cavitermes tuberosus possess a well‐developed frontal gland situated in the frontal projection on their head. The gland produces a blend of unbranched alkenes and alkadienes combined with three diterpene hydrocarbons, derived from a novel bicyclic hydrocarbon skeleton. We characterized the molecular structure of the most abundant of these diterpenes and proposed for it a trivial name, cavitene. We conclude that the evolution of the mandibular snapping has not necessarily been accompanied by the reduction or loss of chemical defensive adaptations and that the two defensive modes are not mutually incompatible. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●● , ●●–●●.     

The nature of the gecko visual pigment

Retinal extracts of the Australian gecko, Phyllurus milii (White), have revealed the presence of a photosensitive pigment, unusual for terrestrial animals, because of its absorption maximum at 524 mµ. This pigment has an absorption spectrum which is identical in form with that of other visual chromoproteins. It is not a porphyropsin, for bleaching revealed the presence, not of retinene₂, but of retinene₁ as a chromophore. Photolabile pigments with characteristics similar to those of the Phyllurus visual pigment were also detected in retinal extracts of six other species of nocturnal geckos. The presence of this retinal chromoprotein adequately accounts for the unusual visual sensitivity curve described by Denton for the nocturnal gecko. This pigment may have special biological significance in terms of the unique phylogenetic position of geckos as living representatives of nocturnal animals which retain some of the characteristics of their diurnal ancestors. The occurrence of this retinene₁ pigment, intermediate in spectral position between rhodopsin and iodopsin, is interpreted in support of the transmutation theory of Walls. The results and interpretation of this investigation point up the fact that, from a phylogenetic point of view, too great an emphasis on the duplicity theory may serve to detract attention from the evolutionary history of the retina and the essential unitarianism of the visual cells.