Evolutionary significance of ontogenetic colour change in animals

Ontogenetic colour changes are non-reversible colour changes associated with normal progressive development of an individual of a species. This paper provides the first review of the evolutionary significance of this phenomenon in animals. Proximate mechanisms and environmental cues are briefly discussed and a conceptual framework for understanding the ultimate reasons for ontogenetic colour change is established. Changes in size, vulnerability, reproductive status, habitat and metabolism are often associated with ontogenetic colour change and can aid in understanding its adaptive significance. Neutral or non-adaptive ontogenetic colour changes due to phylogenetic inertia and developmental constraints are also considered. Existing studies of ontogenetic colour changes in marine invertebrates, terrestrial invertebrates, fish, amphibians, reptiles, birds and mammals are discussed within this framework. A need is identified for more experimental tests of hypotheses for the significance of ontogenetic colour change.     

The shape of compass termite mounds and its biological significance

Summary In northern Australia, compass termites build tall wedge-shaped mounds with an elongated axis that has a striking north-south orientation. Various hypotheses have been advanced to account for this remarkable mound architecture. However, behavioural aspects of mound orientation have rarely been investigated. The currently accepted hypothesis considers mound orientation as an adaptation to local long-term environmental conditions to maintain a temperature plateau at the eastern face of the mound. According to this hypothesis termites should concentrate at the eastern face when ambient temperature conditions are not ideal. This was tested in the current study by applying a new, non-destructive technique that allows monitoring of termites through solid material. Termatrac®, a tool developed for termite pest detection, uses microwaves to detect the movement of termites. As predicted by the eastern- face-plateau hypothesis, termites concentrated in the morning at the eastern face of the mound. However, this pattern was not found at sunrise or noon despite a similar temperature gradient between eastern and western face. This might indicate that only the morning heating of the eastern face is important for the termites, while it plays no prominent role during the rest of the day. The eastern-face-plateau hypothesis is then compared with other hypotheses to develop a general framework that addresses the different characteristics of compass mound architecture: shape, orientation and geographic variation in orientation.Received 1 November 2002; revised 28 January 2003; accepted 12 February 2003.     

Stability of behavioral syndromes but plasticity in individual behavior: consequences for rockfish stock enhancement

This study investigated behavioral syndromes, which are defined as correlations between behaviors. Behavioral syndromes can lead to the unintentional alteration of a wide range of behavioral traits of hatchery fish if unintentional selection on one behavior leads to selection on a correlated behavior. Specifically, this study used brown rockfish, Sebastes auriculatus, to test the hypothesis that a fish that feeds at high rates in the absence of a predator also takes more risks when a predator is present, and that through such a correlation, unintentional hatchery selection for high feeding rates may also lead to changes in risk taking behavior (here defined as behavior that increases predation risk). Behavioral syndromes were found—feeding behavior in the absence of a predator tended to correlate positively with both feeding behavior in the presence of a predator model and time near the model. These syndromes were stable through time—that is, the same correlations appeared 10 days later when the behavioral assays were repeated. However individual behavior was inconsistent (plastic). A fish could both feed and take risks at high rates on Day 1, but then both feed and take risks at low rates on Day 10. Thus, while behavioral syndromes were stable (i.e. present in both rounds 1 and 2), individuals were plastic in their behavior (i.e. inconsistent between rounds 1 and 2). After 16 weeks of hatchery rearing, neither growth nor survival were predicted by behavior. It is suggested that the behavioral plasticity within individuals through time makes consistent selection for strong feeders less likely, and that species with more plastic behavior may be less susceptible to unintentional selection on behavioral syndromes than species with behavior that is more fixed.     

Seasonal phenotypic plasticity of wing melanisation in the cabbage white butterfly, Pieris rapae L. (Lepidoptera: Pieridae)

Abstract.  1. Effective thermoregulation is crucial for the fitness of small flying insects. Phenotypic plasticity of the ventral hindwing of pierid butterflies is widely recognised as adaptive for effective thermoregulation. Butterflies eclosing in cooler environments have more heavily melanised wings that absorb solar radiation, thus allowing flight under these cool conditions.
2. Many pierids also exhibit phenotypic plasticity of dorsal forewing melanisation but in this case, cooler environments reduce melanisation. It has been hypothesised that this plasticity is also adaptive because it increases solar reflection from the wing surfaces onto the body in certain basking postures.
3. The degree of seasonal variation in ventral hindwing and dorsal forewing melanisation of wild-caught Pieris rapae was quantified to determine if it shows patterns of plasticity similar to that documented for other Pieris species.
4. Male wing melanisation on both wing surfaces shows the characteristic seasonal, adaptive plasticity. However, only some dorsal forewing pattern elements of females conformed to the predictions of the hypothesis of adaptive dorsal forewing melanisation. Sexual dimorphism of wing pattern plasticity may result from, and/or affect, sexual dimorphism of behaviour and physiology of these butterflies.     

Thermal characterization of butterfly wings—1. Absorption in relation to different color, surface structure and basking type

1. 1. Spectral integral reflectance, transmittance and the resulting absorption of intact and descaled butterfly wings of the black-winged Pachliopta aristolochiae (Papilionidae), the white-winged Pieris brassicae (Pieridae), and the yellow-winged Gonepteryx rhamni (Pieridae) were determined between 350 and 800 nm.

2. 2. Whereas in the black forewing of the dorsal basking Pachliopta almost all incident light is absorbed nearly independent of the wavelength and thus converted into heat, the white forewing of the body basking Pieris absorbs less than 20% in the visible range of the spectrum.

3. 3. The yellow hindwing of the lateral basking Gonepteryx absorbs to a higher degree than the Pierid wing, but—due to the sparsely arranged scales—transmittance is clearly increased (40–50% between 525 and 800 nm).

4. 4. The varying thermal characteristics of the different wings with reference to the color and arrangement of the scales and the different basking strategies of the butterflies are discussed.

Phenotypic flexibility in the energetic strategy of the greater white-toothed shrew,Crocidura russula

The balance between energetic acquisition and expenditure depends on the amount of energy allocated to biological functions such as thermoregulation, growth, reproduction and behavior. Ambient temperature has a profound effect on this balance, with species inhabiting colder climates often needing to invest more energy in thermoregulation to maintain body temperature. This leads to local behavioral and physiological adaptations that increase energetic efficiency. In this study, we investigated the role of activity, behavior and thermogenic capacity in the ability of the greater white-toothed shrew, Crocidura russula, to cope with seasonal changes. Individuals were captured in the Sintra-Cascais Natural Park, a Mediterranean region, and separated into three experimental groups: a control group, acclimated to a 12L:12D photoperiod and temperature of 18–20 °C; a winter group, acclimatized to natural winter fluctuations of light and temperature; and a summer group, acclimatized to natural summer fluctuations of light and temperature. No differences were found in resting metabolic rate and nonshivering thermogenesis between the three groups. However, winter shrews significantly reduced their activity, particularly at night, compared to the control and summer groups. Differences in torpor use were also found between groups, with winter shrews entering torpor more frequently and during shorter periods of time than summer and control shrews. Our results indicate C. russula from Sintra relies on the flexibility of energy saving mechanisms, namely daily activity level and torpor use, to cope with seasonal changes in a Mediterranean climate, rather than mechanisms involving body heat production.     

Evening light exposure to computer screens disrupts human sleep,biological rhythms,and attention abilities

The use of electronic devices with light-emitting screens has increased exponentially in the last decade. As a result, humans are almost continuously exposed to unintentional artificial light. We explored the independent and combined effects of two aspects of screen illumination, light wavelength, and intensity, on sleep, its biological regulation, and related functional outcomes. The 2 × 2 repeated-measure design included two independent variables: screen light intensity (low ([LI] versus high [HI]) and wavelength (short [SWL] versus long [LWL]). Nineteen participants (11F, 8M; mean age 24.3 [±2.8] years) underwent four light conditions, LI/SWL, HI/SWL, LI/LWL, and HI/LWL, in counterbalanced order. Each light exposure lasted for two hours (21:00–23:00), following which participants underwent an overnight polysomnography. On each experimental night, oral temperature and urine samples (for melatonin analysis) were collected at multiple time points. Each morning, participants filled out questionnaires and conducted a computerized attention task. Irrespective of light intensity, SWL illumination significantly disrupted sleep continuity and architecture and led to greater self-reported daytime sleepiness. SWL light also altered biological rhythms, subduing the normal nocturnal decline in body temperature and dampening nocturnal melatonin secretion. Light intensity seemed to independently affect sleep as well, but to a lesser degree. Both light intensity and wavelength negatively affected morning attention. In sum, light wavelength seems to have a greater influence than light intensity on sleep and a wide-range of biological and behavioral functions. Given the widespread use of electronic devices today, our findings suggest that screen light exposure at evening may have detrimental effects on human health and performance.     

Thermal tolerance and recovery behaviour of Thorectes lusitanicus (Coleoptera,Geotrupidae)

1. Population differences in physiological responses are examined in Thorectes lusitanicus, an endemic Iberian dung beetle species, by submitting individuals of different populations to the same experimental and acclimation conditions. 2. An infrared thermography protocol was used, consisting of three assays: start of activity, cold response, and heat response. Individuals of 12 populations were studied and the comparative explanatory capacities of several environmental factors in relation to the observed inter‐population differences were examined. 3. The heating rate from chill coma to the beginning of activity was the variable with the highest discrimination power among the studied populations, accounting for 94% of the observed variance. Regarding the heat response, only six of the 16 thermal variables reached significance (inter‐population differences accounted for 52–74% in these six thermal parameters). 4. From the three considered environmental factors (Mediterranean climate, land cover, and trophic characteristics) only land cover characteristics remain statistically significant, affecting the cold response of individuals. 5. Thorectes lusitanicus is a species characterised by a high diversity of thermotolerance and recovery traits across populations with a low degree of association with broad environmental factors. Finally, it is suggested that the apterous character of this species could be a determinant factor explaining the high diversity of ecophysiological traits related to thermal stress tolerance and the recovery time.