Optimization of cryptic coloration in heterogeneous habitats

We present a theoretical approach to the optimization of crypsis in heterogeneous habitats. Our model habitat consists of two different microhabitats, and the optimal combination of crypsis in the microhabitats is supposed to maximize the probability of escaping detection by a predator. The probability of escaping detection for a prey is a function of: (i)degree of crypsis, (ii) probability of occurrence in the microhabitats and (iii) probability of encountering a predator in the microhabitats. Because crypsis is background-specific there is a trade-off between crypsis in two visually different microhabitats. Depending on the nature of the trade-off, the optimal coloration is either a compromise between the requirements of the differing microhabitats or entirely adapted to only one of them. An increased risk of predation in one of the microhabitats favours increased crypsis in that microhabitat. Because the trade-off constrains possible optimal solutions, it is not possible to predict the optimal coloration only from factors (i)-(iii). However, habitat choice may fundamentally change the situation. If minimizing predation risk does not incur any costs, the prey should exclusively prefer the microhabitat where it has a lower probability of encountering a predator and better crypsis. The implications of these results for variation in cryptic coloration and polymorphism are discussed.     

Long-term ozone effects on vegetation, microbial community and methane dynamics of boreal peatland microcosms in open-field conditions

To study the effects of elevated ozone concentration on methane dynamics and a sedge species, Eriophorum vaginatum, we exposed peatland microcosms, isolated by coring from an oligotrophic pine fen, to double ambient ozone concentration in an open‐air ozone exposure field for four growing seasons. The field consists of eight circular plots of which four were fumigated with elevated ozone concentration and four were ambient controls. At the latter part of the first growing season (week 33, 2003), the methane emission was 159±14 mg CH₄ m^?2 day^?1 (mean±SE) in the ozone treatment and 214±8 mg CH₄ m^?2 day^?1 under the ambient control. However, towards the end of the experiment the ozone treatment slightly, but consistently, enhanced the methane emission. At the end of the third growing season (2005), microbial biomass (estimated by phospholipid fatty acid biomarkers) was higher in peat exposed to ozone (1975±108 nmol g^?1 dw) than in peat of the control microcosms (1589±115 nmol g^?1 dw). The concentrations of organic acids in peat pore water showed a similar trend. Elevated ozone did not affect the shoot length or the structure of the sedge E. vaginatum leaves but it slightly increased the total number of sedge leaves towards the end of the experiment. Our results indicate that elevated ozone concentration enhances the general growth conditions of microbes in peat by increasing their substrate availability. However, the methane production did not reflect the increase in the concentration of organic acids, probably because hydrogenotrophic methane production dominated in the peat studied. Although, we used isolated peatland microcosms with limited size as study material, we did not find experimental factors that could have hampered the basic conclusions on the effects of ozone.     

Mating distribution and its temporal dynamics affect operational sex ratio: a simulation study

The present study investigated how variation in mating distribution in time and among males influences the operational sex ratio (OSR) with a simulation inspired by paternally caring fish. Varying (1) the potential reproductive rate of each sex, (2) the mating distribution among males, and (3) the length of male mating phase, we created different mating patterns. In each case, we searched for the adult sex ratio that resulted in an OSR of 50% (where sex-roles switch). This approach enabled a comparison with a previous model. We found that the OSR was influenced by the distribution of matings in time and among males when the male mating phase was limited by a parental phase. Furthermore, the mating dynamics were shaped by the fact that the numbers of males and females and their capacities for collateral investment affected OSR immediately from the start of the reproductive season, whereas their times-out had a delayed effect on OSR.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 551–559.     

Incrimination of Phiebotomus papatasi as vector of Leishmania major in the southern Jordan Valley

he status of sandflies as vectors of cutaneous leishmaniasis in the southern Jordan Valley was investigated during 1992. Sandflies were collected from domestic habitats and from burrows of Psammomys obesus . Of 686 Phlebotomus papatasi females collected from burrows, fourteen harboured promastigotes in their guts. On the other hand, none of 1446 P.papatasi females collected from domestic habitats were found infected. The highest infection rate (5.5%) was recorded in November at the end of the sandfly season. Six leishmanial stocks isolated from P.papatasi females were typed by cellulose acetate electrophoresis using the six enzymes G6PDH, 6PGDH, PGI, PGM, FK and ME. Five of the leishmanial stocks were identical to a Leishmania major reference strain (MHOMISU/73/5-ASKH). The sixth isolate was a 6PGDH variant of L.major . These findings present the first direct evidence of the role of P.papatasi as a vector of L.major in Jordan.     

Climate control on the long-term anomalous changes of zooplankton communities in the Northwestern Mediterranean

In marine ecosystems, pelagic copepods, chaetognaths and jellyfish play a key role in matter and energy flow. While copepods support most food webs and the biological pump of carbon into the deep ocean, chaetognaths and jellyfish may affect the strength of the top-down control upon plankton communities. In this study, we show that the main events in the long-term variability of these functional groups in the Northwestern Mediterranean were tightly linked to changes of climate forcing of the North Atlantic sector. Large-scale climate forcing has altered the pelagic food-web dynamics through changes in biological interactions, competition and predation, leading to substantial changes manifested as bursts or collapses in zooplankton populations, and consequently to a major change ca. 1987. These events become more frequent in the 1980s and the early 1990s in the studied zooplankton functional groups suggesting a shift in the functioning of the pelagic ecosystem. The environmental modifications and the results reported here are therefore, indicators of a regime change pointing to a more regeneration-dominated system in the study area. We suggest a chain of mechanisms, whereby climate variation has modified the long-term dynamics of pelagic copepods, chaetognaths and jellyfish in the Ligurian Sea.     

Seasonal shifts in the diet of lake zooplankton revealed by phospholipid fatty acid analysis

1. We analysed the phospholipid fatty acid (PLFA) profiles of seston and of the dominant zooplankter, Daphnia longispina, through the open water period in a small, dystrophic lake to investigate seasonal variation in the diet of Daphnia. Phytoplankton, heterotrophic bacteria, green sulphur bacteria and methane‐oxidizing bacteria (MOB) were all present in the water column of the lake, and previous studies have indicated that vertically migrating Daphnia can exploit all these potential food sources. 2. For adult Daphnia, although there was some correspondence between the PLFA profile of Daphnia and the concurrent seston PLFA profile, strongest correlations were between the Daphnia PLFA profile and those of potential food sources determined 7 days earlier. This interval presumably reflects the time it takes for adult Daphnia to turn over their fatty acid pool. 3. A correlation between the concentration of polyunsaturated fatty acids (PUFAs) in the epi‐ and metalimnion and measured primary production indicated that, within the total PLFA fraction, PUFAs can be useful biomarkers for phytoplankton in food‐web studies. Algal PUFAs contributed appreciably to total PLFAs in adult Daphnia during spring and summer, but less so in autumn. 4. Daphnia in the lake actually reached their highest biomass in autumn, when methanotrophic activity was also highest, and the highest magnitude of MOB‐specific PLFAs was recorded in both adult and juvenile Daphnia. A strong relationship existed between δ¹³C values of Daphnia reported previously and the proportion of MOB‐specific PLFAs in Daphnia. Autumnal mixing evidently stimulates bacterial oxidation of methane from the hypolimnion, and exploitation of the methanotrophic bacteria sustains a high Daphnia population late in the season. 5. Our results show that the PLFA composition of freshwater zooplankton like Daphnia corresponds rather well to that of their in situ diet of phytoplankton and bacteria, with a lag period of around 1 week in the case of adult animals. The PLFA profile of seston revealed the dominant available food sources, and relating these to the Daphnia PLFA profile provided insights into seasonal changes in Daphnia diet.