Alate production in an aphid in relation to ant tending and alarm pheromone

1. Winged dispersal is vital for aphids as predation pressure and host plant conditions fluctuate. 2. Ant‐tended aphids also need to disperse, but this may represent a cost for the ants, resulting in an evolutionary conflict of interest over aphid dispersal. 3. The combined effects of aphid alarm pheromone, indicating predation risk, and ant attendance on the production of winged aphids were examined in an experiment with Aphis fabae (Homoptera: Aphididae) (Scopoli 1763) aphids and Lasius niger (Formicidae: Formicinae) (Linné, 1758) ants. 4. This study is the first to investigate the joint effects of alarm pheromone and ant attendance, and also the first to detect an influence of alarm pheromone on the production of winged morphs in A. fabae. 5. After a period of 2 weeks, it was found that aphid colonies exposed to intermittent doses of alarm pheromone produced more winged individuals, whereas ant tending had the opposite effect. The effects were additive on a log scale, and ant attendance had a greater proportional influence than exposure to alarm pheromone. A tentative conclusion is that ants have gained the upper hand in an evolutionary conflict about aphid dispersal.     

Effect of Applied and Endogenous Auxin on Callus and Root Formation of In Vitro Shoots of the Apple: Rootstocks M26 and A2

The influence of exogenous IBA (indol-3yl-butyric acid) on rootand callus formation was studied in shoots of the apple rootstocksA2 and M26. The shoots grown in vitro were derived originallyfrom meristems of both juvenile and adult trees. Endogenousindol-3yl-acetic acid (IAA) concentrations in leaves and stemswere correlated with the responses to applied IAA. After 30 subcultures shoots from A2 and M26 rooted easily, butA2 did so more readily and even without IBA. Treatment withIBA improved percentage rooting and number of roots in bothrootstocks. Ex-adult and ex-juvenile shoots of A2 formed rootsto the same extent. However, ex-adult shoots of A2 showed ahigher IBA optimum for root number than ex-juvenile A2 and werealso less sensitive to supra-optimal IBA concentrations. Incontrast, in M26, there were no differences between ex-adultand ex-juvenile shoots. The results imply that rooting ability is associated more withdifferences between cultivars than with the origin of the explants.The best rooting occurred in ex-adult shoots of A2 which hadthe lowest endogenous IAA concentration, while callus formationwas correlated with high endogenous auxin concentration. Ex-adultA2 produced almost no callus even after exposure to high IBAconcentrations (25µM) whereas ex-adult M26 formed muchmore callus at 1/10 of the IBA concentration. Malus sylvestris (L.) Mill. var. domestica Borkh., Malus pumila Mill., apple rootstocks A2 and M26, in vitro culture, root and callus formation, HPLC analyses of IAA     

Revision of the Clinopodium abyssinicum group (Labiatae)

A tropical African group of species commonly included in the genus Satureja is revised and moved to the genus Clinopodium . Satureja abyssinica (Benth.) Briq. ssp. abyssinica and ssp. condensata (Hedberg) Seybold, S. paradoxa (Vatke) Engl. ex Seybold, S. robusta (Hook.f) Brenan and S. vernayana Brenan should be known under the following names: Clinopodium abyssinicum (Hochst. ex Benth.) Kuntze var. abyssinicum and C. abyssinicum var. condensatum (Hedberg) Ryding, C. paradoxum (Vatke) Ryding, C. robustum (Hook.f) Ryding and C. vernayanum (Brenan) Ryding, respectively. Satureja cacondensis (G. Taylor) Brenan, S. masukuensis (Baker) Eyles and S. myriantha (Baker) Brenan, including its varieties, are amalgamated and should be known by the name Clinopodium myrianthum (Baker) Ryding.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 391–408.     

Effects of long‐term fox baiting on species composition and abundance in an Australian lizard community

Abstract We report on the effects of almost a decade of 1080‐fox baiting on a lizard community in a mosaic Australian habitat. Replicated comparisons of baited versus non‐baited control areas with near‐identical histories of bush fires, grazing and climate showed a higher density of red fox tracks (Canis vulpes) in the non‐baited areas. Furthermore, the fox‐baited areas showed a more than five times higher density of sand goannas (Varanus gouldii), a species that strongly overlaps the red fox in food niche breadth and is itself a direct target of fox predation, in particular its eggs and young. Exclusion of predators from a natural habitat led to significant increases in the density of small lizards, suggesting that predation can drive lizard population dynamics in this ecosystem. Replicated pitfall‐trapping in three habitats in the control areas (with high fox and low goanna density) versus the baited areas (with low fox and high goanna density) showed that fox baiting had positive effects on the density of diurnal scincid lizards in open grassland, whereas the control areas showed higher density of nocturnal gecko lizards. Our interpretation is that fox removal may result in a shift in the top predator towards the sand goanna. Historically, this indigenous, endemic species was the natural top predator. It has co‐evolved with its prey and that may have moulded it into a more efficient lizard predator per encounter than the introduced fox.     

The Effects of Breeder Loss on Wolves

Abstract Managers of recovering wolf (Canis lupus) populations require knowledge regarding the potential impacts caused by the loss of territorial, breeding wolves when devising plans that aim to balance population goals with human concerns. Although ecologists have studied wolves extensively, we lack an understanding of this phenomenon as published records are sparse. Therefore, we pooled data (n = 134 cases) on 148 territorial breeding wolves (75 M and 73 F) from our research and published accounts to assess the impacts of breeder loss on wolf pup survival, reproduction, and territorial social groups. In 58 of 71 cases (84%), ≥1 pup survived, and the number or sex of remaining breeders (including multiple breeders) did not influence pup survival. Pups survived more frequently in groups of ≥6 wolves (90%) compared with smaller groups (68%). Auxiliary nonbreeders benefited pup survival, with pups surviving in 92% of cases where auxiliaries were present and 64% where they were absent. Logistic regression analysis indicated that the number of adult-sized wolves remaining after breeder loss, along with pup age, had the greatest influence on pup survival. Territorial wolves reproduced the following season in 47% of cases, and a greater proportion reproduced where one breeder had to be replaced (56%) versus cases where both breeders had to be replaced (9%). Group size was greater for wolves that reproduced the following season compared with those that did not reproduce. Large recolonizing (>75 wolves) and saturated wolf populations had similar times to breeder replacement and next reproduction, which was about half that for small recolonizing (≤75 wolves) populations. We found inverse relationships between recolonizing population size and time to breeder replacement (r= —0.37) and time to next reproduction (r= —0.36). Time to breeder replacement correlated strongly with time to next reproduction (r=0.97). Wolf social groups dissolved and abandoned their territories subsequent to breeder loss in 38% of cases. Where groups dissolved, wolves reestablished territories in 53% of cases, and neighboring wolves usurped territories in an additional 21% of cases. Fewer groups dissolved where breeders remained (26%) versus cases where breeders were absent (85%). Group size after breeder loss was smaller where groups dissolved versus cases where groups did not dissolve. To minimize negative impacts, we recommend that managers of recolonizing wolf populations limit lethal control to solitary individuals or territorial pairs where possible, because selective removal of pack members can be difficult. When reproductive packs are to be managed, we recommend that managers only remove wolves from reproductive packs when pups are ≥6 months old and packs contain ≥6 members (including ≥3 ad-sized wolves). Ideally, such packs should be close to neighboring packs and occur within larger (≥75 wolves) recolonizing populations.     

Chastity belts in gartersnakes: the functional significance of mating plugs

Male red-sided gartersnakes (Tfiamnophis sirtalis parietalis) deposit a thick gelatinous plug that occludes the female cloaca after copulation. Previous workers have interpreted the plug as a sexually-selected adaptation to (1) physically prevent re-mating by the female, and/or (2) provide pheromonal cues to discourage courtship by rival males or to decrease receptivity by females. Our data support the former hypothesis, but not the latter. Plugs serve as effective physical barriers to additional copulation for <72 h, but this is long enough for most females to become unreceptive, and/or disperse from the mating aggregation. Experimental removal of plugs immediately after copulation results in some re-mating by females, but plug removal several hours later does not rekindle sexual receptivity. Contrary to previous work, our experiments show that fluids associated with copulation (rather than the plug per se) are responsible for the rapid decline of male interest in mated females. Thus, the plug's primary function is to physically prevent matings rather than as a source of pheromonal cues to manipulate the behaviour of females or rival males. Plug mass is determined not only by a male's body size, but by his prior mating history (plug mass decreases with repeated mating) and by the size of his partner (males allocate larger plugs to larger females). Gartersnakes are unusual not only in their production of mating plugs, but also in their brief duration of copulation compared to other snakes. Mating plugs may have evolved in gartersnakes to reduce mating times, because of the extremely high 'opportunity cost' of prolonged mating to a male gartersnake in a mating aggregation.     

Gut length plasticity in perch: into the bowels of resource polymorphisms

Resource polymorphisms, intraspecific variation in morphology due to differential resource use, are common across a wide range of animal taxa. The focus in studies of such polymorphisms has been on external morphology, but the differential use of food resources could also influence other phenotypic traits such as the digestive performance. In the present study, we experimentally demonstrate that Eurasian perch ( Perca fluviatilis L.) display adaptive plasticity in gut length when exposed to different food types. Perch fed a less digestible food type developed relatively longer guts compared to fish fed a more easily digested food type. This divergence in gut length was also apparent under natural conditions because perch inhabiting the littoral and pelagic habitats of a lake differed in resource use and relative gut length. Despite that the digestive system in perch is plastic, we found that individuals switching to a novel food type might experience an initial fitness cost of the diet switch in the form of a temporary reduction in body condition. These results show the importance of gut length plasticity for an ontogenetic omnivore but also a cost that might prevent diet switching in polymorphic populations.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 517–523.     

Crosses between frog populations reveal genetic divergence in larval life history at short geographical distance

A number of studies have documented interpopulation divergence in amphibian larval life-history traits across latitudes. Because many frogs are philopatric and have a patchy habitat distribution, genetic divergence could also exist on a much smaller geographical scale, revealed by recent estimates of population divergence using molecular markers. Whether this divergence is reflected in phenotypic traits is virtually unknown. Using artificial fertilization, individuals of the common frog, Rana temporaria , were crossed from two populations situated 130 km apart and differing in population size. The pattern of size at metamorphosis showed evidence of non-additive effects, as demonstrated by a significant interaction between male and female population of origin. Outbreeding resulted in an increase in metamorph size when eggs from the small population were fertilized with sperm from the large population. In the reciprocal cross, however, the pattern was in the opposite direction, with no significant effect of male population of origin. Genetic divergence of populations separated by a relatively short geographical distance may be more common in frogs than previously acknowledged, with potential implications for conservation of declining amphibian species.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 189–195.     

Larval aestivation and direct development as alternative strategies in the speckled wood butterfly, Pararge aegeria, in Sweden

ABSTRACT.

• 1 Sweden has two disjunct populations of the speckled wood butterfly, Pararge aegeria L. The southern population has two generations per year but the central Swedish population is univoltine. When rearing larvae from central Sweden under normal photoperiodic conditions but at temperatures slightly above the ambient, 42% of the larvae developed directly and produced a second generation of adults the same summer. The egg—larval development time of the directly developing individuals was about 40 days, whereas that of the individuals developing along the univoltine pathway was about 100 days.
• 2 Larvae of the central Swedish population normally aestivate during part of the summer even though abundant food is available. In the closely related Lasiommata petropolitana F., which is the only Swedish satyrid that overwinters in the pupal stage besides P.aegeria, larvae do not aestivate, indicating that there does not seem to be any obligatory association between pupal hibernation and larval aestivation.
• 3 Development rates of aestivating and directly developing P.aegeria are equal up to the third larval instar. During the third and fourth instars, however, the development rate of aestivating individuals is retarded and females also have an additional fifth instar.
• 4 Since the central Swedish P.aegeria have the capacity to develop directly, and the southern Swedish ones have the capacity to aestivate, the evidence indicates that the outcome of the cost/benefit balance of univoltine versus bivoltine development differs between the two areas.

     

Synergistic selection and graded traits

Fitness interactions where benefits are shared only between individuals with similar traits are often referred to as synergistic. Examples include defence characters, like insect warning colouration and plant unpalatability, and joint activities needing the active participation of all group members, such as cooperative hunting. Previous analyses, assuming discrete variation in the trait, have shown that synergistic selection can be a sufficient explanation for the evolutionary stability of such traits. Here, we investigate the consequences of graded variation in the trait responsible for synergistic effects. Classifying the synergism as unbiased when an individual receives maximum associational benefit by having the same trait value as its neighbours, and letting a positive (negative) bias represent the maximum above (below) this value, we show that only positively biased synergistic selection can enhance a graded trait. Thus for graded traits, a synergistic benefit is not in itself sufficient for evolutionary stability. We study possible reasons for synergistic bias in a simple model of plant defences against herbivores, and suggest that the processes of herbivore avoidance learning and diet selection are probable causes of positive bias. We propose that mammalian herbivores exposed to a given level of toxicity will show stronger feeding aversion to higher toxicity, resulting in positively biased synergistic selection of plant defence traits. Positive bias produced by avoidance learning may, in a similar way, also select for defence signals.