Exploring the relationship between tychoparthenogenesis and inbreeding depression in the Desert Locust, Schistocerca gregaria

Tychoparthenogenesis, a form of asexual reproduction in which a small proportion of unfertilized eggs can hatch spontaneously, could be an intermediate evolutionary link in the transition from sexual to parthenogenetic reproduction. The lower fitness of tychoparthenogenetic offspring could be due to either developmental constraints or to inbreeding depression in more homozygous individuals. We tested the hypothesis that in populations where inbreeding depression has been purged, tychoparthenogenesis may be less costly. To assess this hypothesis, we compared the impact of inbreeding and parthenogenetic treatments on eight life-history traits (five measuring inbreeding depression and three measuring inbreeding avoidance) in four laboratory populations of the desert locust, Schistocerca gregaria, with contrasted demographic histories. Overall, we found no clear relationship between the population history (illustrated by the levels of genetic diversity or inbreeding) and inbreeding depression, or between inbreeding depression and parthenogenetic capacity. First, there was a general lack of inbreeding depression in every population, except in two populations for two traits. This pattern could not be explained by the purging of inbreeding load in the studied populations. Second, we observed large differences between populations in their capacity to reproduce through tychoparthenogenesis. Only the oldest laboratory population successfully produced parthenogenetic offspring. However, the level of inbreeding depression did not explain the differences in parthenogenetic success between all studied populations. Differences in development constraints may arise driven by random and selective processes between populations. (Résumé d'auteur

The Life Cycle Relative to Temperature of Protaphorura Armatus (Tullberg) (Collembola: Onychiuridae), a Parathenogenetic Species

Apparent parthenogenetic reproduction in Collembola has sometimes been attributed to accidental transfer of spermatophores with the food material from one culture to another (Schaller, 1953; Mayer, 1957). Conclusive evidence of parthenogenesis has only in recent years been accumulated for a number of species of Collembola, of which some were found in field populations consisting entirely of females (Choudhuri, 1958; Huther, 1961; Marshall and Kevan, 1962; Petersen, 1965; 1971 ; Snider, 1973). In Onychiuridae, parthenogenesis is apparently quite common. Onychiurus parthenogeneticus Choudhuri and Tullbergia krausbaueri (Bomer) undoubtedly reproduce in the absence of males (Choudhuri, 1958; Hale, 1966; Petersen, 1971); so does Tullbergia granulata Mills, where individuals reared in isolation from the time of hatching invariably lay viable eggs (unpublished observations). Large females of Onychiurus procampatus Gisin 1956 breed through a form of thelytokous parthenogenesis (Hale, 1964). The size groupings found in O. procarnpatus (two sizes of females and only small males) were also observed in O. firnatus Gisin 1952 and O. quadriocellatus Gisin 1947 and may indicate the existence of both parthenogenetic and sexually reproducing forms in these species (Hale, 1964). Recent laboratory observations on Protaphorura armatus (Tullberg) revealed that this species too reproduces parthenogenetically. The present study was undertaken to investigate the effect of temperature on the biology of the species

Simulated emergence of cyclic sexual-asexual reproduction

Motivated by the cyclic pattern of reproductive regimes observed in some species of green flies (``{\it aphids}''), we simulate the evolution of a population enduring harsh seasonal conditions for survival. The reproductive regime of each female is also seasonal in principle and genetically acquired, and can mutate for each newborn with some small probability. The results show a sharp transition at a critical value of the survival probability in the winter, between a reproductive regime in the fall that is predominantly sexual, for low values of this probability, or asexual, for high values.Comment: 9 pages, 4 figures, requires RevTe

Life history of Monocystis parasites and genetic diversity of their hosts, the invasive Amynthas earthworms

Monocystis is a parasites in the phylum Apicomplexa that infects nearly 100% of earthworms; however, the parasites have low survivorship, low production of transmissible gametocysts, and seemingly lack schizogony. The purpose of this study was to investigate the improbable lifecycle and life history traits of a Monocystis species of the invasive Asian earthworms, Amynthas agrestis and A. tokioensis in Vermont. Preliminary data suggested that Monocystis sp. vary in life history traits between three sites sampled; therefore, it was necessary to investigate the genetic diversity and the mating system of its host, as the mating system is responsible for genetic variation. Random Amplified Polymorphic DNA (RAPD) markers revealed genetic variation within and among sites of both Amynthas spp. which appear to employ a mixed-mating system of both sexual and asexual reproduction demonstrated by the presence of both clonal and unique genotypes. The life history and life cycle of Monocystis sp. in A. agrestis was described by using microscopy to measure phenology and parasite stages and numbers. Amynthas spp. at Audubon had a shorter season and the parasites produced gametocysts earlier than at the other two sites. The parasite success rate at Audubon, Hort Farm, and Centennial Woods were 113.8%, 73.6%, and 0%, repectively. Audubon worms had higher numbers of gametocyts but a lower mean number of sporocysts per gametocyst (127.0) than did hosts at Hort Farm (145.8). Monocystis sp. has different life history traits and schedules to compensate for the length of the season and the genetic variation of its host

A comparative study on the functional response of Wolbachia-infected and uninfected forms of the parasitoid wasp Trichogramma brassicae

Trichogramma species (Hymenoptera: Trichogrammatidae) are haplo-diploid egg parasitoids that are frequently used as biological control agents against lepidopteran pests. These wasps display two reproductive modes, including arrhenotoky (bisexuality) and thelytoky (unisexuality). Thelytokous forms are often associated with the presence of endosymbiotic Wolbachia bacteria. The use of thelytokous wasps has long been considered as a way to enhance the efficacy of biological control. The present study investigates the potential of a thelytokous Wolbachiainfected and an arrhenotokous uninfected Trichogramma brassicae Bezdenko strain as inundative biocontrol agents by evaluating their functional response towards different egg densities of the factitious host, the Angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae). The results revealed a type II functional response for both strains in which parasitism efficiency decreases with host egg density because of an increasing host handling time. A model with an indicator variable was used to compare the parameters of Holling’s disc equation in different data sets. It was demonstrated that the two strains did not differ in host attack rate. However, the Wolbachia-infected strain did have an increased host handling time when compared to the bisexual strain. Some applied aspects of the findings are discusse

Hybridisation generates a hopeful monster: a hermaphroditic selfing cichlid

Compared to other phylogenetic groups, self-fertilization (selfing) is exceedingly rare in vertebrates and is known to occur only in one small clade of fishes. Here we report observing one F1 hybrid individual that developed into a functional hermaphrodite after crossing two closely related sexually reproducing species of cichlids. Microsatellite alleles segregated consistent with selfing and Mendelian inheritance and we could rule out different modes of parthenogenesis including automixis. We discuss why selfing is not more commonly observed in vertebrates in nature, and the role of hybridisation in the evolution of novel trait

Complex taxonomy and global phylogeography of the well-known tropical earthworm Pontoscolex corethrurus

Few earthworm species are peregrine and among them, Pontoscolex corethrurus is the most well-known. Probably native from the Guyana shield, this earthworm is nowadays distributed worldwide, in the tropical and sub-tropical zones. It is found in a wide range of habitats, from apparently pristine to any kind of human-disturbed environments. P. corethrurus presents several characteristics of a successful invader: r-strategy, parthenogenesis reproduction and ecological and reproductive plasticity. Although its ecological interactions with the environment were well documented, the taxonomic status of this earthworm was unclear. We investigated the phylogenetic relationships within the genus Pontoscolex at a global scale (25 countries), focusing on morphologically indistinguishable lineages using the mitochondrial COI and 16S markers, the nuclear ITS 2 and 28S markers and a large-scale multilocus sequence data matrix obtained using the Anchored Hybrid Enrichment (AHE) phylogenomic method. Four cryptic species were discovered within the P. corethrurus species complex and one of them, P. corethrurus L1 was particularly widespread. Although sympatry between L1, L3 and L4 was observed, no case of hybridization was detected between L1 and the two other cryptic species, confirming the status of species of P. corethrurus L1. A population genetics study of this species using COI sequences and AFLP data revealed a low mitochondrial genetic diversity and a high proportion of clones in some populations, in accordance with the principal mode of reproduction of the species (i.e., parthenogenesis). However, variable levels of genetic diversity among populations and results of gametic disequilibrium analysis suggesting recombination in several populations, confirmed a mixed-mating strategy (sexual reproduction and parthenogenesis)