Sexual dichromatism and male colour morph in ultraviolet-B reflectance in two populations of the jumping spider Phintella vittata (Araneae: Salticidae) from tropical China

In the literature on animal use of ultraviolet (UV) vision and UV reflectance, it has usually been UV-A (315–400 nm) that is considered. Animals are generally assumed to be unable to discriminate UV-B (280–315 nm) from other wavelengths in natural sunlight. Recently, some animals are known to be able to detect and respond directly to UV-B in order to avoiding exposure to it. However, there is no evidence that the hue corresponding to UV-B is salient to an animal during intraspecies communication. Using Phintella vittata , an ornate jumping spider from two geographically different populations in China, we investigated geographical, intersexual, intrasexual, and interpopulation variation in UV reflectance. We found that both the males and the females of P. vittata reflect UV light, and that the reflection bands are located in UV-B, a part of reflectance spectrum never previously investigated. We also found a great deal of population variation in the UV-B spectral reflectance. Furthermore, two colour morphs, the 'green' and 'yellow' morphs, are identified for adult males for both populations, and both morphs differ greatly in both UV-B and human-visible wavelengths. This is the first demonstration of a UV-B reflecting salticid and UV-B sexual dichromatism.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 7–20.     

Phytoplankton and its dynamics in two tropical lakes: a tropical and temperate zone comparison

Temporal patterns of phytoplankton biomass and community structure are described for two Kenyan lakes and subsequently compared with patterns reported in other tropical and temperate lakes. Lake Naivasha had a lower and more seasonally variable (10×) biomass, with a seasonal shift between diatoms and blue-greens, while the L. Oloidien biomass was less variable (3.7×) and dominated by blue-greens. Biomass and chlorophyll a were strongly correlated and in turn were coupled to the level of total phosphorus. A total of 143 and 94 taxa were described for L. Naivasha and L. Oloidien, respectively.The comparative analysis showed: a) a paucity of exclusively tropical species; b) that more than 30 percent of the species in two highly saline Kenyan lakes were also present in the two freshwater lakes; c) no evidence for a postulated decline of phytoplankton species abundance with latitude from the temperate zone to the tropics; d) that the low fraction of chrysophyte biomass in tropical lakes is a function of trophy rather than of latitude; e) that the fraction of chlorophyte biomass in tropical lakes is generally higher than in temperate lakes; f) that the proportion of nannoplankton in the two Kenyan freshwater lakes is not different from that in temperate lakes of the same trophy; g) that seasonal or annual biomass oscillations in the tropics are not systematically lower than in the temperate zone; h) evidence for large inter-year difference in the max.:min. biomass ratio in the only tropical lake (L. Naivasha) for which such data are available; i) that an average biomass ratio appears predictable for tropical lakes from the proportion of the sediment surface in contact with epilimnetic water. Overall, no evidence was found that the freshwater tropical phytoplankton composition or dynamics differ in any fundamental fashion from that observed in the temperate lakes during the summer.Contribution number 147 of the Limnology Research Centre, McGill University.     

Object detection in the fly during simulated translatory flight

Translatory movement of an animal in its environment induces optic flow that contains information about the three-dimensional layout of the surroundings: as a rule, images of objects that are closer to the animal move faster across the retina than those of more distant objects. Such relative motion cues are used by flies to detect objects in front of a structured background. We confronted flying flies, tethered to a torque meter, with front-to-back motion of patterns displayed on two CRT screens, thereby simulating translatory motion of the background as experienced by an animal during straight flight. The torque meter measured the instantaneous turning responses of the fly around its vertical body axis. During short time intervals, object motion was superimposed on background pattern motion. The average turning response towards such an object depends on both object and background velocity in a characteristic way: (1) in order to elicit significant responses object motion has to be faster than background motion; (2) background motion within a certain range of velocities improves object detection. These properties can be interpreted as adaptations to situations as they occur in natural free flight. We confirmed that the measured responses were mediated mainly by a control system specialized for the detection of objects rather than by the compensatory optomotor system responsible for course stabilization. Accepted: 20 March 1997     

Seeing the Past: Visual Media in Archaeology

As digital media become increasingly affordable and accessible, visual representation in archaeology is expanding across several dimensions. In this essay, I examine some emerging forms of visual media in archaeology, including online documentaries, maps and photographs, hypermedia, experimental films, and peripatetic video. Visual media offer powerful opportunities for engagement with the public. In addition, archaeologists are finding new ways to use the visual in interpretation, analysis, and critique. Experimental visual works often are self-consciously reflexive, questioning and exposing the ways archaeological knowledge is constructed, represented, and disseminated.     

Vision and visual variation in the peacock blenny

Microspectrophotometry (MSP) revealed the presence of a rod and at least two cone classes (mid‐ and long‐wavelength sensitive) in the intertidal peacock blenny Salaria pavo . Both rhodopsin and porphyropsin based visual pigments were found in all fish, together with high individual variation in the chromophore ratio. The three morphs (females, males and sneaker males) differed in their spectral sensitivities (as measured with the optomotor response) with sneakers having higher sensitivity at long‐wavelengths than either males or females. This long‐wave displacement of peak sensitivity could be due to elevated proportions of porphyropsin visual pigments in the sneakers' retinae. The lenses of all morphs exhibited a short‐wavelength cut‐off and an unusual layer of carotenoid was found behind the retinal pigment epithelium and in the outer segments of some cones. These screening pigments could serve a photo‐protective role or to improve visual contrast. No short‐wave photoreceptors were located using MSP. This indicates that this cone class may be absent or present at very low numbers in the retina. This is the first in depth study of the visual system of a blenniid fish and indicates potential within‐species visual variation that may be related to the species' habitat and morph‐specific behavioural requirements.     

Activation of cholecystokinin neurons in the dorsal pallium of the telencephalon is indispensable for the acquisition of chick imprinting behavior

Chick imprinting behavior is a good model for the study of learning and memory. Imprinting object is recognized and processed in the visual wulst, and the memory is stored in the intermediate medial mesopallium in the dorsal pallium of the telencephalon. We identified chicken cholecystokinin (CCK)-expressing cells localized in these area. The number of CCK mRNA-positive cells increased in chicks underwent imprinting training, and these cells expressed nuclear Fos immunoreactivity at high frequency in these regions. Most of these CCK-positive cells were glutamatergic and negative for parvalbumin immunoreactivity. Semi-quantitative PCR analysis revealed that the CCK mRNA levels were significantly increased in the trained chicks compared with untrained chicks. In contrast, the increase in CCK- and c-Fos-double-positive cells associated with the training was not observed after closure of the critical period. These results indicate that CCK cells in the dorsal pallium are activated acutely by visual training that can elicit imprinting. In addition, the CCK receptor antagonist significantly suppressed the acquisition of memory. These results suggest that the activation of CCK cells in the visual wulst as well as in the intermediate medial mesopallium by visual stimuli is indispensable for the acquisition of visual imprinting.     

An experimental system to study ecophysiological responses of submerged macrophytes to temperature and light

An experimental growth system was devised to study the ecophysiological responses of submerged macrophytes to temperature and light. Using the system, a pilot study was conducted to compare responses to light of three representative species common to the littoral zone of Lake Biwa: Vallisneria asiatica Miki var. biwaensis Miki, which is endemic to Japan, Potamogeton maackianus A. Benn., a dominant submerged macrophyte in Lake Biwa, and Elodea nuttallii (Planch.) St. John, one of the most influential submerged exotic macrophytes naturalized in Japan. Different relative growth rate responses and other growth parameters among the species were observed. We ascertained the experimental system to be useful for the comparison of ecophysiological responses of submerged macrophytes.     

Orthologous comparison in a gene-rich region among grasses reveals stability in the sugarcane polyploid genome

Modern sugarcane (Saccharum spp.) is an important grass that contributes 60% of the raw sugar produced worldwide and has a high biofuel production potential. It was created about a century ago through hybridization of two highly polyploid species, namely S. officinarum and S. spontaneum. We investigated genome dynamics in this highly polyploid context by analyzing two homoeologous sequences (97 and 126 kb) in a region that has already been studied in several cereals. Our findings indicate that the two Saccharum species diverged 1.5-2 million years ago from one another and 8-9 million years ago from sorghum. The two sugarcane homoeologous haplotypes show perfect colinearity as well as high gene structure conservation. Apart from the insertion of a few retrotransposable elements, high homology was also observed for the non-transcribed regions. Relative to sorghum, the sugarcane sequences displayed colinearity, with the exception of two genes present only in sorghum, and striking homology in most non-coding parts of the genome. The gene distribution highlighted high synteny and colinearity with rice, and partial colinearity with each homoeologous maize region, which became perfect when the sequences were combined. The haplotypes observed in sugarcane may thus closely represent the ancestral Andropogoneae haplotype. This analysis of sugarcane haplotype organization at the sequence level suggests that the high ploidy in sugarcane did not induce generalized reshaping of its genome, thus challenging the idea that polyploidy quickly induces generalized rearrangement of genomes. These results also confirm the view that sorghum is the model of choice for sugarcane.