Asymmetric Phenotypes of Sterile Hybrid Males From Reciprocal Crosses Between Species of the Anopheles gambiae Complex

Haldane’s rule of speciation states that sterility or inviability affects the heterogametic sex of inter-species hybrids. Darwin’s corollary to Haldane’s rule implies that there are asymmetric phenotypes in inter-species hybrids from reciprocal crosses. Studying the phenotypes of F1 hybrids among closely related species of malaria mosquitoes can assist researchers in identifying the genetic factors and molecular mechanisms of speciation. To characterize phenotypes of sterile hybrid males in the Anopheles gambiae complex, we performed crosses between laboratory strains of An. merus and either An. gambiae or An. coluzzii. The reproductive tracts had normal external morphology in hybrid males from crosses between female An. merus and male An. gambiae or An. coluzzii. Despite being sterile, these males could copulate with females for a normal period of time and could transfer a mating plug to induce female oviposition and monogamy. In contrast, the entire reproductive tracts in hybrid males from crosses between female An. gambiae or An. coluzzii and male An. merus were severely underdeveloped. These males had atrophic testes and reduced somatic organs of the reproductive system including male accessary glands and ejaculatory duct. In addition, hybrid males with underdeveloped reproductive tracts displayed a shorter copulation time with females and failed to induce female oviposition and monogamy due to their inability to form and transfer a plug to females during mating. The asymmetry of the phenotypes associated with hybrid male sterility suggests that different genetic factors and molecular mechanisms are responsible for reproductive isolation in reciprocal crosses among species of the An. gambiae complex.

Description of a new natural Sonneratia hybrid from Hainan Island, China

Here, we describe, illustrate and compare a new natural hybrid, Sonneratia × zhongcairongii Y. S. Wang & S. H. Shi (Sonneratiaceae), with its possible parent species. Based on its morphological characteristics and habitat conditions, this taxon is considered to represent a sterile hybrid between S. alba and S. apetala. In China, the new hybrid is only reported in the mangrove forest in Dongzhai Harbour, Hainan Island. It has intermediate characteristics with its parents by elliptical leaf blades, peltate stigma, terminal or axillary inflorescence with 1–3 flower dichasia, cup – shaped calyx (4–6 calyx lobes) and no petals. We also provide a key for the identification of Sonneratia species.

A common suite of cellular abnormalities and spermatogenetic errors in sterile hybrid males in Drosophila

When two species interbreed, the resulting hybrid offspring are often sterile, with the heterogametic (e.g. XY) hybrid usually being more severely affected. The prevailing theory for this pattern of sterility evokes divergent changes in separate lineages having maladaptive interactions when placed together in a hybrid individual, with recessive factors on the sex chromosome interacting with dominant factors on the autosomes. The effect of these interactions on gametogenesis should not be uniform across species pairs unless genetic divergence follows the same paths in different lineages or if a specific stage of gametogenesis is more susceptible to detrimental genetic interactions. Here, we perform a detailed cellular characterization of hybrid male sterility across three recently diverged species pairs of Drosophila . Across all three pairs, sterile hybrid sperm are alive but exhibit rapid nuclear de-condensation with age, with active, but non-differentiated, mitochondria. Surprisingly, all three sets of interspecies hybrids produce half of the number of sperm per round of spermatogenesis, with each sperm cell containing two tails. We identify non-disjunction failures during meiosis I as the likely cause. Thus, errors during meiosis I may be a general phenomenon underlying Drosophila male sterility, indicating either a heightened sensitivity of this spermatogenic stage to failure, or a basis to sterility other than the prevailing model.

Investigation of the Guinea fowl and domestic fowl hybrids as potential surrogate hosts for avian cryopreservation programmes

In the last decade, avian gene preservation research has focused on the use of the early precursors of the reproductive cells, the primordial germ cells (PGCs). This is because avian PGCs have a unique migration route through the vascular system which offers easy accessibility. Furthermore, culturing of the cells in vitro, freezing/thawing, reintegration into a recipient embryo and the development of the germ cells can be carried out in well-defined laboratory circumstances. The efficient recovery of the donor genotype and the frequency of germline transmission from the surrogate host animals are still areas which need further development. Thus, the aim of the present study was to investigate an infertile interspecific hybrid (recipient) as an appropriate host for primordial germ cells from native poultry breeds. Guinea fowl × chicken hybrids were produced, the crossing was repeated inversely. The phenotype, the hatching time, the hatching rate, the sex ratio, the presence of own germ cells, the fertility and the phenotype of viable hybrids and the incidence of chromosomal abnormalities of dead hybrid embryos were described. 6.65% viable offspring was obtained with crossing of Guinea fowl females with domestic fowl males. Crossing of domestic fowl hens with Guinea fowl male resulted in lower fertility, 0.14% viable offspring. Based on the investigations, the observed offspring from the successful crossing were sterile male hybrids, thus an extreme form of Haldane’s rule was manifested. The sterile hybrid male embryos were tested by injecting fluorescently labeled chicken PGCs. The integration rate of labeled PGCs was measured in 7.5-day, 14.5-day and 18.5-day old embryonic gonads. 50%, 5.3% and 2.4% of the injected hybrid embryos survived and 40%, 5.3% and 2.4% of the examined gonads contained fluorescent labeled donor PGCs. Therefore, these sterile hybrid males may be suitable recipients for male PGCs and possibly for female PGCs although with lower efficiency. This research work shows that the sterility of hybrids can be used in gene conservation to be a universal host for PGCs of different avian species.

Neuroaxonal Dystrophy in a mule: first case reported

ABSTRACT A 12-month-old mule (sterile hybrid equine species) presented unspecific neurological changes (symmetric ataxia, dysmetria, conscious proprioceptive deficit and weakness). Due to poor prognosis and to the fact that a sibling from the previous generation exhibited similar clinical signs that were not definitively diagnosed, the animal was euthanized. Diagnosis of neuroaxonal dystrophy was confirmed by anatomohistopathological analysis. This is the first clinical case of neuronal dystrophy in a mule reported in the world. The clinical and histopathological characteristics of this disease were very similar to those reported for several equine breeds. Therefore, the disease should also be considered in the diagnosis of neurological conditions in mules and donkeys.

Isoetes ×gopalkrishnae (Isoetaceae), a new interspecific sterile hybrid from central India

Isoetes ×gopalkrishnae hybr. nov., is described, illustrated and compared with possible parent species. Based on morphological characteristics and habitat conditions, this taxon is considered to represent a sterile hybrid between I. coromandelina and I. panchananii. The new hybrid is amphibious and grows on the exposed shore of an artificial pond. It is known only from a single locality on the Vindhya plateau in Uttar Pradesh, India. It can be distinguished from other taxa by a combination of characters including the lack of a scale, the leaf which is terete in transverse section, velum absent to rudimentary, a sporangial wall with internal pigmentation, rugulate megaspores with a smooth equatorial girdle and microspores with densely echinate to short-cristate ornamentation. It is the first Isoetes hybrid reported from the Indian subcontinent.

A new hybrid of Tectaria (Tectariaceae) from southern China

A new natural hybrid, Tectaria × hongkongensis (Tectariaceae), is described and illustrated from Hong Kong, China. It is a sterile hybrid supported by the abortive spores and cytological data [2n = 120 (3x)]. This hybrid is morphologically somewhat similar to T. zeilanica in the small size of plants, strongly dimorphic leaves, the shape of sterile fronds, and acrostichoid sporangia. Molecular data indicate its maternal parent is probably T. harlandii. Tectaria × hongkongensis is the first hybrid confirmed by morphological and cytological evidence in East Asia.