Decision rules, energy metabolism and vigour of hermit-crab fights

Aggressive interactions between animals are often settled by the use of repeated signals that reduce the risk of injury from combat but are expected to be costly. The accumulation of lactic acid and the depletion of energy stores may constrain activity rates during and after fights and thus represent significant costs of signalling. We tested this by analysing the concentrations of lactate and glucose in the haemolymph of hermit crabs following agonistic interactions over the ownership of the gastropod shells that they inhabit. Attackers and defenders play distinct roles of sender and receiver that are fixed for the course of the encounter. Attackers perform bouts of 'shell rapping', which vary in vigour between attackers and during the course of the encounter, and are a key predictor of victory. In contrast to the agonistic behaviour of other species, we can quantify the vigour of fighting. We demonstrate, to our knowledge for the first time, an association between the vigour of aggressive activity and a proximate cost of signalling. We show that the lactate concentration in attackers increases with the amount of shell rapping, and that this appears to constrain the vigour of subsequent rapping. Furthermore, attackers, but not defenders, give up when the concentration of lactate is high. Glucose levels in attackers also increase with the amount of rapping they perform, but do not appear to influence their decision to give up. Defenders are more likely to lose when they have particularly low levels of glucose. We conclude that the two roles use different decision rules during these encounters.     

Aphids in a changing world: testing the plant stress,plant vigour and pulsed stress hypotheses

• 1 The plant stress, plant vigour and pulsed stress hypotheses describe the relationships between drought stress, plant quality and herbivore performance. We used an aphid‐Brassica system to test these hypotheses under different drought treatments.
• 2 The quantity of water added per plant/week was 75%, 50% and 25% of the control (unstressed) water regime for low, medium and high drought stress, respectively, and 50% applied fortnightly for pulsed drought stress. The performance of a ‘senescence’ (generalist) and a ‘flush’ feeder (specialist) aphid species and host plant quality were assessed.
• 3 Drought treatments had a similar effect on the fecundity and intrinsic rate of increase of both aphid species. Aphid performance on unstressed and highly drought‐stressed plants was significantly lower compared with medium drought stress. On average, 20% greater fecundity and 40% greater intrinsic rates of increase were recorded for both aphid species at medium drought stress compared with unstressed plants.
• 4 Plant biomass and relative water contents were significantly greater for unstressed plants compared with high and pulsed drought treatments. Foliar nitrogen concentration was significantly greater in the high drought stress and pulsed treatments, and the dominant glucosinolate (glucobrassicin) concentration was significantly greater in drought stress treatments.
• 5 The present study supports the plant stress hypothesis, although the plant vigour and pulsed stress hypotheses are not supported by our data. The implications of these findings for plant–herbivore interactions under changing environmental conditions are discussed.

     

Decoupling vigour and quality in the autumn colours game: Weak individuals can signal, cheating can pay

According to the coevolution theory, autumn colours are a warning signal to insects, signalling the level of chemical defences or availability of nutrients. Because in the original model tree vigour and defences were positively correlated, it is not clear whether signalling would still be stable when they are decoupled, and the fact that weak trees often display bright autumn colours is usually presented as evidence against the coevolution theory. I show that in a theoretical model of insect-tree coevolution, signalling is still stable when vigour and defences are decoupled. Weak trees can signal. Moreover, partial cheating is possible. The different equilibria depend on the importance of vigour and defences against insect attack, of vigour in the production of the signal, and of pleiotropic effects between colour and defences. These results provide precise predictions that can be used for planning future empirical test.     

Phospholipid meets all-trans-retinal: the making of RPE bisretinoids

The lipid phase of the photoreceptor outer segment membrane is essential to the photon capturing and signaling functions of rhodopsin. Rearrangement of phospholipids in the bilayer accompanies the formation of the active intermediates of rhodopsin following photon absorption. Furthermore, evidence for the formation of a condensation product between the photolyzed chromophore all-trans-retinal and phosphatidylethanolamine indicates that phospholipid may also participate in the movement of the retinoid in the membrane. The downside of these interactions is the formation of bisretinoid-phosphatidylethanolamine compounds that accumulate in retinal pigment epithelial cells with age and that are particularly abundant in some retinal disorders. The propensity of these compounds to negatively impact on the cells has been linked to the pathogenesis of some retinal disorders including juvenile onset recessive Stargardt disease and age-related macular degeneration.     

Display vigour and subsequent fight performance in the siamese fighting fish,betta splendens

The display of 24 individual male Siamese fighting fish to an unresponsive stimulus conspecific was measured, and the fish were then placed together in pairs. For 11 of the 12 pairs, the outcome of the aggressive interaction which ensued was predicted by the gill cover erection durations obtained in the pre-fight isolate tests. The implications of this result for theories of display function are discussed.     

Novel perennial ryegrass-Neotyphodium endophyte associations: relationships between seed weight,seedling vigour and endophyte presence

Two forage cultivars of perennial ryegrass (Lolium perenne) colonised by the mutualistic fungal endophyte Neotyphodium lolii, strain AR37, were used to investigate relationships between seed weight, seed vigour and endophyte presence. Seed was separated into six fractions according to weight, with each fraction divided into two further groups with the first being subject to accelerated ageing. Seed germination rates and proportions of viable and total endophyte frequencies were assessed for each fraction. Heavier fractions of seed produced a higher number of endophyte infected seedlings sooner than the lighter fractions for both cultivars. The highest proportion of viable endophyte was found in the fastest germinating perennial ryegrass seed for all weight fractions, from both cultivars, indicating a strong relationship between endophyte presence and seed germination rate. For one of the cultivars, after accelerated ageing, as seed weight increased the proportion of viable endophyte increased and the discrepancy between the proportion of endophyte in fresh and accelerated aged seed was reduced. This implies that for this cultivar heavier ryegrass seed provides a more favourable habitat to the dormant endophyte than lighter seed during storage and/or allowed for a greater biomass of endophyte hyphae to proliferate in the seed tissues prior to seed dormancy, thus allowing the fungus to develop more propagules and greater nutritional reserves.     

The relationship between ions, vigour and salinity tolerance of Acacia seeds

Seeds of A. bivenosa DC. Prod., A. coriacea DC., A. elata A. Cunn. Ex Benth., A. farnesiana (L.) Willd., A. nilotica Willd. ex Del., A. salicina Lindl., A. saligna (Labill.) H. Wendle., A. senegal (L.) Willd., A. tortilis (Forsk.) Hayne and A. tumida F. Muell. ex Benth. were tested for their final germination percentage (FG) in distilled water (DW) and in 25–400 mol m^-3 NaCl, germination rate (1/t₅₀, where t₅₀ is the time to 50% of final germination in DW), Ca and K concentration (Ca_unt, K_unt), the leakage of these ions when soaked for 24 h in DW (Ca_DW, K_DW) and the leakage (additional to that in DW) when soaked in 250 mol m^-3 NaCl (Ca_NaCl, K_NaCl). Linear regression revealed significant positive relationships between salinity tolerance (I₅₀, the concentration of NaCl required to reduce final germination to 50% of the control value in DW) and FG, Rate, Ca_unt/K_unt and Ca_NaCl/K_NaCl. There was also a significant negative relationship between I₅₀ and K_unt. Multiple regression equations were developed to predict I₅₀ from the above parameters. Equations based on (1) FG and Rate, (2) Ca_unt and K_unt, and (3) any of these four factors, accounted for 61, 60 and 79%, respectively, of the variation in I₅₀. Further equations, introducing the leakage of ions into DW and NaCl and the ratios of ion concentrations monitored, improved the predictive value of the equation. The best equation, accounting for 93% of the variation was: I₅₀ = 108 + 422 Rate − 1.32 K_unt + 16.3 Ca_DW − 5.4 K_DW + 71.6 K/Ca_DW. These equations provide a screening test for salt tolerance of Acaciaseed germination based on simple and rapid laboratory chemical analyses and germination tests. This revised version was published online in June 2006 with corrections to the Cover Date.     

Seed vigour and water relations in wheat

The laboratory germination (criterion radicle emergence) of seven seed lots of winter wheat cv. Slejpner was similar. However, they differed in vigour as demonstrated by differences in germination after controlled deterioration carried out at a range of seed moisture contents, at two temperatures and for different times. A vigour assessment for each lot was quantified by calculating a value for the seed lot constant K_i, of the viability equation. Germination in lower water potentials reduced the uptake of water, radicle and coleoptile emergence and radicle and coleoptile extension. There was no difference in the water uptake of seed lots differing in vigour. However, seed lots of lower vigour showed less radicle emergence, less coleoptile emergence and shorter radicles than higher vigour seed lots in low water potentials. Similarly, controlled deterioration resulted in reduced radicle and coleoptile emergence and growth compared to unaged seed, and also to a greater sensitivity to low water potentials. The implications for field establishment are discussed.     

Impacts of two point mutations of RPE65 from Leber's congenital amaurosis on the stability, subcellular localization and isomerohydrolase activity of RPE65

RPE65, a membrane-associated protein in the retinal pigment epithelium, is the isomerohydrolase essential for regenerating 11-cis retinal, the chromophore for visual pigments. RPE65 mutations are associated with inherited retinal dystrophies. Here we report that single point mutations of RPE65, Y144D and P363T, identified in patients with Leber's congenital amaurosis (LCA), significantly decreased the stability of RPE65. Moreover, these mutations altered subcellular localization of RPE65 and abolished its isomerohydrolase activity. These observations suggest that the decreased protein stability and altered subcellular localization of RPE65 may represent a mechanism for these mutations to lead to vision loss in LCA patients.     

The relation between hybrid vigour and genotype-environment interactions

Summary Consideration was given to the response curves and response surfaces that are obtained when genotypes are grown at various levels of environmental factors. These curves and surfaces were used to illustrate genotype-environment interactions and possible relations between two parents and their F ₁.When a hybrid had a response exactly intermediate between its parents, the metric values for the hybrid were not intermediate but varied with the environment, exhibiting different degrees of dominance including overdominance (hybrid vigour). A range in dominance for the metric also was found when the response of the hybrid was more similar to one parent than the other.A hybrid with an intermediate response has a lower phenotypic variance across environments than the mean variance of its parents. In some situations the hybrid's variance is less than that of either parent.A component of the error variation for a genotype was shown to vary with the environment having a minimal value when the environment was optimal.An algebraic treatment of response curves and surfaces was presented. In some instances the metric values for two parents and their F ₁ in a range of environments may be related in the form of a multiple regression.     

Segmental vitiligo as the possible expression of cutaneous somatic mosaicism: implications for common non-segmental vitiligo

Clinical findings in vitiligo challenge the widely accepted organ specific autoimmune pathomechanisms. We draw the attention to the fact that the distribution of segmental vitiligo (SV) fits in at least a subset of patients a pattern usually associated with cutaneous mosaicism. The association of SV to non-segmental vitiligo (NSV) now confirmed by several observations indicates a continuum between the two subsets with shared predisposing genetic factors, including genes operating specifically in the skin. Some pedigrees associating SV and NSV further suggest a mechanism of loss of heterozygosity for a dominant gene controlling part of the cutaneous phenotype. The mosaic hypothesis applies only to SV and to the rare SV-NSV association, but suggests that predisposing genetic factors in common NSV should also be searched directly in the skin. SV would be a good candidate disease to explore as a proof of principle of a new gene discovery strategy useful for multigenic disorders with organ specificity, applicable in priority to chronic inflammatory skin disorders.