Assortative mating across a hybrid zone in Chorthippus parallelus (Orthoptera: Acrididae)

Two subspecies of the grasshopper Chorthippus parallelus meet and form a hybrid zone in the Pyrenees. Both strong hybrid dysfunction and a behavioural difference occur, which would seem to make the zone a suitable candidate for speciation by reinforcement. One of the classic ways of looking for this is to test for increased levels of assortative mating between populations from close to the region of contact. Here we show that, with virgin insects, such assortment decreases as one approaches the centre of the zone in C. parallelus. The pattern is different upon remating, with non-virgins showing a pattern more like that predicted by reinforcement. Overall there is little evidence for reinforcement. We argue that other tests of the model may be more appropriate for stable hybrid zones.     

Chromosome Inversion Polymorphisms Influence Morphological Traits in <Emphasis Type="Italic">Trimerotropis Pallidipennis</Emphasis> (Orthoptera)

Trimerotropis pallidipennis is a New World grasshopper whose South-American populations are polymorphic for six pericentric inversions. Previous work has demonstrated that the frequences of these inversions correlate with climatic variables, and hence a possible adaptive pattern was put forward. In the present work we analysed a sample of a natural population of T. pallidipennis to ascertain whether the chromosomal inversions have effects on exophenotypes. Two hundred and sixty-eight males coming from a natural population at Uspallata, Mendoza Province, Argentina were analysed, and it was observed that most inversions had significant effects on phenotypes. Furthermore, some body size-related characteristics (such as tegmina length) were correlated with the number of inversions. Individuals from populations at higher altitude or latitude (i.e., at lower minimum temperatures), along with higher frequencies of standard sequences, were significantly smaller, and this coherence between interpopulational with intrapopulational results may indicate that the diminished body size of the standard sequence-carrying individuals may be caused by an effect of the inversions, or genes within the inversions, on body size. We finally put forward the hypothesis that reduced body size in a context of reduced minimum temperature may be a response to shortened development season, and so smaller individuals may be advantageous.     

Taxonomic status of the grasshopper Podisma tyatiensis and reproductive isolation between P. tyatiensis and Podisma sapporensis

The grasshopper Podisma tyatiensis, which is distributed only at the summit of Mount Tyatya on Kunashiri Island, the Kuril Islands, is closely related to Podisma sapporensis, which has a broad distribution range on the islands of northern Japan and the Russian Far East (Hokkaido, Sakhalin and Kunashiri). The present study examined the taxonomic status of P. tyatiensis by crossing P. tyatiensis males with P. sapporensis females from Sakhalin. More than 90% of eggs from intrapopulation crosses developed to at least the last embryonic stage, whereas only 64% of eggs from the interpopulation crosses developed into that embryonic stage. Cytogenetic observations of prediapause embryos showed that the interpopulation crosses always led to the production of unfertilized eggs, and that all of the developing embryos had the maternal genome only. A mixture of haploid and diploid cells of maternal origin was found in most of those embryos. This result shows that unfertilized eggs produced by P. sapporensis females from Sakhalin developed parthenogenetically to at least the embryonic stage before hatching. The present crossing experiments revealed a high level of incompatibility between the genomes of the Sakhalin population and the Tyatya population, and confirmed the full species status of P. tyatiensis.     

Body size and elevation: do Bergmann's and Rensch's rule apply in the polytypic bushcricket Poecilimon veluchianus?

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Vitellogenin Titres in Normal and Accelerated Maturation of Gregarious-Phase Schistocerca gregaria

Isolation of vitellogenin of the Schistocerca gregaria (Forskal) in its gregarious phase was achieved by a combination of gel permeation and anion exchange chromatography. Staining for carbohydrate and lipid moieties showed that the vitellogenin is a glycolipoprotein. The vitellogenin of S. gregaria has a native molecular weight of about 700 kDa. On SDS-PAGE, the protein showed nine apoproteins of about 124, 120, 105, 60, 59, 58, 57, 53 and 34 kD. Determination of the levels of vitellogenin by ELISA in the haemolymph of maturing females showed that those exposed to mature males from 1 to 2 days after ecdysis had increased levels of vitellogenin from day 10 (81.1 ± 4.5). In contrast, females exposed to immature males or kept alone showed an increase (107.3 ± 0.9 and 70.2 ± 2.7) not until day 16 or later, respectively. These results are consistent with the accelerating effect of pheromonal emissions from mature males on the maturation of female S. gregaria.     

Structure of male accessory glands of Bolivarius siculus (fischer) (Orthoptera,Tettigoniidae) and protein analysis of their secretions

In Tettigoniidae (Orthoptera), male reproductive accessory glands are involved in the construction of a two‐part spermatophore; one part, the spermatophylax, is devoid of sperm and considered a nuptial gift. The morphology, ultrastructure, and secretion protein content of the male reproductive accessory glands from Bolivarius siculus were investigated. Two main groups of gland tubules open into the ejaculatory duct: the “first‐order” glands, a number of large anterior tubules, and the “second‐order” glands, smaller and more numerous tubules positioned posteriorly. Along with a further subdivision of the gland tubules, we here describe for the first time an additional gland group, the intermediate tubules, which open between first and second‐order glands. The mesoderm‐derived epithelium of all glands is a single layer of microvillated cells, which can be either flattened or cylindric in the proximal or distal region of the same gland. Epithelial cells, very rich in RER and Golgi systems, produce secretions of both electron‐dense granules and globules or electron‐transparent material, discharged into the gland lumen by apocrine or merocrine mechanisms, respectively. With one exception, a unique electrophoresis protein profile was displayed by each of the gland types, paralleling their unique morphologies. To assess the contribution of different types of accessory glands to the construction of the spermatophore, the protein patterns of the gland secretions were compared with those of the extracts from the two parts of the spermatophore. All samples showed bands distributed in a wide range of molecular weight, including proteins of very low molecular mass. However, one major high molecular weight protein band (>180 kDa) is seen exclusively in extracts from the first‐order glands, and corresponds to an important protein component of the spermatophylax. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Patterns of trait divergence between populations of the meadow grasshopper, Chorthippus parallelus

Abstract.— To understand the process of speciation, we need to identify the evolutionary phenomena associated with divergence between populations of the same species. A powerful approach is to compare patterns of trait differences between populations differing in their evolutionary histories. A recent study of genetic divergence between populations of the meadow grasshopper Chorthippus parallelus , from different locations around Europe has allowed us to use this species to investigate which aspects of evolutionary history are associated with divergence in morphology and mating signals. During the last glaciation C. parallelus was confined to a number of refugia in southern Europe and has subsequently recolonized the northern part of the continent. This process of isolation followed by range expansion has created populations differing markedly in their evolutionary pasts–some have been isolated from one another for thousands of years, others have undergone repeated founder events, and others now live in sympatry with a closely related species. Using laboratory-reared grasshoppers from 12 different populations with a range of evolutionary histories, we quantify differences in morphology, chemical signals, and male calling-song. The observed pattern of divergence between these populations is then compared with the pattern predicted by hypotheses about what drives divergence. This comparison reveals that long periods in allopatry and processes associated with repeated founder events are both strongly associated with divergence.     

Olfactory responses of two species of grasshoppers to plant odours

Electroantennogram (EAG) responses were recorded from two species of oedipodine grasshoppers, Oedaleus decorus asiaticus L. (graminivorous) and Angaracris barabensis Pall. (forbivorous), to volatiles emitted by chopped leaves of ten plant species. Male O. d. asiaticus showed much stronger EAG responses than conspecific females and both sexes of A. barabensis. Sexual differences in EAG responses correspond to different numbers of antennal sensilla of both sexes and to certain behavioural and morphological factors as well. The overall EAG response profiles of the two grasshopper species to the ten plant odours were similar. However, adaptation to host odour might have occurred because of differences in their feeding habits. Females of the graminivorous O. d. asiaticus possess a significantly higher olfactory sensitivity for poaceous plant species than A. barabensis, while the forbivorous A. barabensis showed significantly higher EAG responses to Allium senescens (Liliaceae), and a tendency of high responses to composite plant species in comparison with O. d. asiaticus.     

Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts?

Several anecdotal reports in the literature have suggested that insects parasitized by hairworms (Nematomorpha) commit `suicide' by jumping into an aquatic environment needed by an adult worm for the continuation of its life cycle. Based on 2 years of observations at a swimming pool in open air, we saw this aberrant behaviour in nine insect species followed by the emergence of hairworms. We conducted field and laboratory experiments in order to compare the behaviour of infected and uninfected individuals of the cricket Nemobius sylvestris. The results clearly indicate that crickets infected by the nematomorph Paragordius tricuspidatus are more likely to jump into water than uninfected ones. The idea that this manipulation involved water detection from long distances by infected insects is not supported. Instead, our observations suggest that infected insects may first display an erratic behaviour which brings them sooner or later close to a stream and then a behavioural change that makes them enter the water.     

Florivory by a floriphilic katydid,Phaneroptera brevis,induces changes in a leaf trait in Lantana camara

1. Plants can induce a response when they are attacked by herbivores. Although the induction of responses by herbivory in both flowers and leaves is relatively well studied, whether florivory (feeding of flowers) can also induce responses in flowers and leaves is less well explored and there are still unanswered questions. These include whether plants exhibit different levels of induced responses depending on the length of exposure to the florivores. 2. To address this knowledge gap, this study used a tropical floriphilic katydid, Phaneroptera brevis, and its non‐native food plant, Lantana camara. Nursery experiments were performed in which dry matter content and anthocyanin concentration of the flower (corolla and stamens), leaf dry matter content, and leaf blade punch resistance were measured at three time phases before and after exposing the plant to the katydid individuals for 0–7 days. 3. It was demonstrated that increasing the length (days) of exposure to the katydid individual leads to higher levels of induced plant response (leaf blade punch resistance), but only in the leaves. It was also shown that higher levels of induced plant response owing to the increase in the length of exposure to the katydid individual was not observed beyond the first set of leaves developed after the exposure. 4. These results address the knowledge gap and show that plants can exhibit different levels of induced responses depending on the length of exposure to florivores. This study thus highlights the far‐reaching importance of florivory on plants.