Basis and extent of genetic variability among doubled haploid plants obtained by pollen culture in Nicotiana sylvestris

Summary All diploid plants (doubled-haploid plants: D.H.) regenerated by androgenesis from binucleated pollen grains in Nicotiana sylvestris differ genetically from the original line as far as morphological features and growth rates are concerned. This androgenic variation (A.V.) is under nuclear control and is transmitted continuously by some D.H. for at least four generations of selfing; other D.H. progenies segregate. Further androgeneses carried out on one single D.H. reveal a new variability and increase the drift from the original line. All results cannot be explained by the presence of residual heterozygosity in the original line, and we suggest that most of the A.V. could originate from changes that occur in the DNA of the vegetative pollen grain cell. D.H. resulting from endomitosis of the vegetative cell would be homozygous and stable, whereas D.H. resulting from nuclear fusion between a vegetative and a generative cell would be heterozygous and would segregate in seeds through succeeding generations.     

Segregation of the isozymes of flax genotrophs

The segregation of isozymes of peroxidase and acid phosphatase in progenies of crosses between large (L) and small (S and L₆) flax genotrophs has been determined. The peroxidase isozymes segregated as expected on a simple Mendelian model with a dominant and a recessive allele and with the L genotroph being a homozygous dominant. All the peroxidase isozymes which differed segregated together, so the isozymes are controlled by either a single locus or closely linked loci. The acid phosphatase isozymes in the F₁ were all L type, but the segregations observed in the F₂ were not always consistent with a simple Mendelian model.     

Complementarity of thermoregulatory rhythms in Micropterus salmoides and M. dolomieui

Largemouth (Micropterus salmoide) and smallmouth (M. dolomieui) blackbasses tested in an electronic shuttlebox exhibited behavioral thermoregulatory rhythms which were temporally complementary. With a LD 12 : 12 photoperiod, M. dolomieui exhibited a preferred-temperature peak of 30.1°C during the latter portion of the photophase, when M. salmoides reached a minimum of 27.1°C. M. dolomieui exhibited a minimum of 26.6°C during the latter portion of scotophase, while M. salmoides remained at a significantly higher plateau of about 29°C, with a peak of 29.5°C at the midpoint of scotophase. The phase relations of the thermoregulatory rhythms relative to photoperiod suggest that they are endogenously timed circadian rhythms entrained by photoperiod. The thermotemporal complementarity of these rhythms suggests an aspect of niche segregation between these largely sympatric congeneric species.     

Is coexistence mediated by microhabitat segregation? An in-depth exploration of a fish invasion

Vendace Coregonus albula has invaded the subarctic Pasvik hydrosystem, northern Norway and Russia, after being translocated from its native Finnish range into Lake Inari (Finland), upstream of Pasvik. The development of the invader and the effects on two native lake communities in the upstream and downstream part of the hydrosystem, respectively, have been monitored since 1991. In the upstream lake location, the invader relegated the native whitefish Coregonus lavaretus from the pelagic habitat within a few years. An expected similar development in the downstream location was, however, not observed. Data are presented on the diet and microhabitat use (vertical pelagic zone) for three types of replicated situation: (1) the invader v. the native species, (2) upstream v . downstream lakes and (3) early and late invasion stages, to explore the outcome of the competitive interactions. The use of different microhabitats available within the deeper pelagic zone in the downstream location was observed to have delayed the negative effects on native whitefish, possibly enabling a persistent coexistence between the two species in the pelagic zone of this lake.     

Rapid generation of ecologically relevant behavioral novelty in experimental cichlid hybrids

The East African cichlid radiations are characterized by repeated and rapid diversification into many distinct species with different ecological specializations and by a history of hybridization events between nonsister species. Such hybridization might provide important fuel for adaptive radiation. Interspecific hybrids can have extreme trait values or novel trait combinations and such transgressive phenotypes may allow some hybrids to explore ecological niches neither of the parental species could tap into. Here, we investigate the potential of second‐generation (F2) hybrids between two generalist cichlid species from Lake Malawi to exploit a resource neither parental species is specialized on: feeding by sifting sand. Some of the F2 hybrids phenotypically resembled fish of species that are specialized on sand sifting. We combined experimental behavioral and morphometric approaches to test whether the F2 hybrids are transgressive in both morphology and behavior related to sand sifting. We then performed a quantitative trait loci (QTL) analysis using RADseq markers to investigate the genetic architecture of morphological and behavioral traits. We show that transgression is present in several morphological traits, that novel trait combinations occur, and we observe transgressive trait values in sand sifting behavior in some of the F2 hybrids. Moreover, we find QTLs for morphology and for sand sifting behavior, suggesting the existence of some loci with moderate to large effects. We demonstrate that hybridization has the potential to rapidly generate novel and ecologically relevant phenotypes that may be suited to a niche neither of the parental species occupies. Interspecific hybridization may thereby contribute to the rapid generation of ecological diversity in cichlid radiations.     

X-linked meiotic drive can boost population size and persistence

X-linked meiotic drivers cause X-bearing sperm to be produced in excess by male carriers, leading to female-biased sex ratios. Here, we find general conditions for the spread and fixation of X-linked alleles. Our conditions show that the spread of X-linked alleles depends on sex-specific selection and transmission rather than the time spent in each sex. Applying this logic to meiotic drive, we show that polymorphism is heavily dependent on sperm competition induced both by female and male mating behavior and the degree of compensation to gamete loss in the ejaculate size of drive males. We extend these evolutionary models to investigate the demographic consequences of biased sex ratios. Our results suggest driving X-alleles that invade and reach polymorphism (or fix and do not bias segregation excessively) will boost population size and persistence time by increasing population productivity, demonstrating the potential for selfish genetic elements to move sex ratios closer to the population-level optimum. However, when the spread of drive causes strong sex-ratio bias, it can lead to populations with so few males that females remain unmated, cannot produce offspring, and go extinct. This outcome is exacerbated when the male mating rate is low. We suggest that researchers should consider the potential for ecologically beneficial side effects of selfish genetic elements, especially in light of proposals to use meiotic drive for biological control.     

Distribution of HLA class Ⅰ and class Ⅱ haplotypes in Chinese Han population based on family segregation

HLA haplotype analysis has important application value in human population genetics, anthropological research and HLA matching transplantation. Based on HLA-A, -B, -C, -DRB1 and -DQB1 genotyping data from 663 families including 663 leukemia patients and 991 related donors, the allele frequency (AF) and haplotype frequency (HF) of two-, three- and five-locus haplotype distribution patterns in the Chinese Han population were determined by family segregation. A total of 38 alleles at A locus, 75 alleles at B locus, 35 alleles at C locus, 53 alleles at DRB1 locus and 22 alleles at DQB1 locus were discovered in this population. The frequencies of these alleles were basically consistent with those of previous reports except for some tiny differences. The study found 11 A-C, 15 C-B, 4 B-DRB1 and 11 DRB1-DQB1 two-locus haplotypes with a frequency over 2%. The number of A-C-B and A-B-DRB1 three-locus haplotype with a frequency over 1% were 11 and 3 respectively. The most common HLA-A-C-B-DRB1-DQB1 haplotype (HF>1%) were A*3001-C*0602-B*1302-DR*0701-DQ*0202 (4.30%), A*0207-C*0102-B*4601-DR*0901-DQ*0303 (3.07%), A*3303-C*0302-B*5801-DR*0301-DQ*0201 (1.49%) and A*1101-C*0102-B*4601-DR*0901-DQ*0303 (1.01%). The results are helpful for finding matching donors for hematopoietic stem cell transplant patients and also contribute to transplant immunology, HLA-related diseases, research of human genetics and other fields.     

Ecomorphology of the African felid ensemble: The role of the skull and postcranium in determining species segregation and assembling history

Morphology of extant felids is regarded as highly conservative. Most previous studies have focussed on skull morphology, so a vacuum exists about morphofunctional variation in postcranium and its role in structuring ensembles of felids in different continents. The African felid ensemble is particularly rich in ecologically specialized felids. We studied the ecomorphology of this ensemble using 31 cranial and 93 postcranial morphometric variables measured in 49 specimens of all 10 African species. We took a multivariate approach controlling for phylogeny, with and without body size correction. Postcranial and skull + postcranial analyses (but not skull‐only analyses) allowed for a complete segregation of species in morphospace. Morphofunctional factors segregating species included body size, bite force, zeugopodial lengths and osteological features related to parasagittal leg movement. A general gradient of bodily proportions was recovered: lightly built, long‐legged felids with small heads and weak bite forces vs. the opposite. Three loose groups were recognized: small terrestrial felids, mid‐to‐large sized scansorial felids and specialized Acinonyx jubatus and Leptailurus serval. As predicted from a previous study, the assembling of the African felid ensemble during the Plio‐Pleistocene occurred by the arrival of distinct felid lineages that occupied then vacant areas of morphospace, later diversifying in the continent.