Pollination syndromes evolved under the reciprocal selection of pollinators and plants (coevolution). Here, the two main methods are reviewed which are applied to prove such selection. (i) The indirect method is a cross-lineage approach using phylogenetical trees to understand the phylogeny. Thus, features of single origin can be distinguished from those with multiple origins. Nearly all pollination modes originate in multiple evolutionary ways. (ii) The most frequent pollinators cause the strongest selection because they are responsible for the plant’s most successful reproduction. The European sexually deceptive orchid genus Ophrys provides an example of a more direct way to prove selection because the attraction of a pollinator is species specific. Most members of the genus have remarkably variable flowers. The variability of the signals given off by the flowers enables the deceived pollinator males to learn individual flower patterns. They thus avoid already visited Ophrys flowers, interpreting them as females rejecting them. As the males will not return to these individually recognizable flowers, the pollinators´ learning behavior causes cross-pollination and prevents the orchid’s self-pollination.
We conducted the first detailed investigation of the floral architecture and reproductive biology of two species from the genus Dorstenia, which are poorly known relatives of Ficus (Moraceae). Our aims were to extend and refine knowledge of the understudied genus Dorstenia and to explore possible insights into the evolution of the fig syconium. We characterised four key stages of floral development using light microscopy, scanning electron microscopy and histological staining. Reproductive biology was found to be complex and species‐specific. Both study species are monoecious and produce an inflorescence of minute male and female flowers. Protogyny, associated with a spatial separation of male and female flowers and asynchronous stamen development, was species‐specific, as was seed set. Our results reveal novel insights into the complex reproductive biology of an under‐studied genus in the family Moraceae. We propose that exploring the reproductive biology of Dorstenia and other poorly known Ficus relatives will provide insights into the evolution of the fig syconium – the unique reproductive structure of this economically and ecologically important genus.
Reproduction and maturation in the economically important, but data-deficient, Mustelus minicanis and M. norrisi were analysed using catches of populations exploited by a gillnet fishery during two years in the southern Caribbean Sea. In total, 691 female (mean +/- SD total length-TL of 55.3 +/- 5.8 cm) and 503 male (50.4 +/- 4.9 cm TL) M. minicanis were assessed, with similar to 95% of all specimens deemed mature. Almost 25% of females were gravid (occurring between January and October) and with variable temporal development of up to six embryos (3.3 +/- 1.2), implying protracted temporal parturition. Parity in the sex ratio of embryos, but not in landed catches, suggested sexual segregation across the fished area. The 50% sizes at maturity (M (50)) (+/- SE) were similarly estimated at 45.11 (+/- 0.39) and 45.48 (+/- 0.42) cm TL for females and males, respectively. Relatively fewer (235) M. norrisi were landed, with samples comprising 150 females (82.6 +/- 18.1 cm TL) and 85 males (75.5 +/- 17.7 cm TL). More than 30% of both sexes were immature. Ten percent of females were gravid (up to 11 embryos) and present in catches between October and February, coinciding with the northern hemisphere autumn/winter. Female and male M (50)s were 76.65 (+/- 1.16) and 69.63 (+/- 1.92) cm TL, respectively. The results imply variable inter-specific reproductive plasticity and the need for further life-history studies. Increasing gillnet selectivity might represent a simple precautionary management option for concurrently regulating catches of the smaller-bodied M. minicanis during peak abundances of gravid females and similar-sized juvenile M. norrisi.
A new species of the genus Liurana Dubois, 1986 is described from Medog County, Tibet, China, based on morphological and molecular data. The new species can be differentiated from all other congeners by the following combination of characters: (1) head wider than long; (2) tympanum distinct and large; (3) hindlimb long, tibiotarsal articulation beyond tip of snout when adpressed; (4) belly with flat tubercles, cloacal region with small tubercles; (5) transverse bands distinctly on dorsal limbs, four bands on thigh and three on tibia; and, (6) dark brown marbled patterns or speckles on white belly. Here, we also discuss the distribution pattern of Liurana in the East Himalaya region, the role of the Yarlung Tsangpo River in the speciation and genetic isolation of congeners, the direct developmental mode of reproduction, and the two different ecotypes of the genus. Lastly, we provide conservation recommendations for the genus in southeastern Tibet.
Populations on islands often exhibit lower levels of genetic variation and ecomorphological divergence compared to their mainland relatives. While phenotypic differentiation in characters, such as size or shape among insular organisms, has been well studied, insular differentiation in quantitative reproductive traits involved in chemical communication has received very little attention to date. Here, we investigated the impact of insularity on two syntopic bumblebee species pairs: one including species that are phylogenetically related (Bombus terrestris and B. lucorum), and the other including species that interact ecologically (B. terrestris and its specific nest inquiline B. vestalis). For each bumblebee species, we characterized the patterns of variation and differentiation of insular (Corsican) vs. mainland (European) populations (i) with four genes (nuclear and mitochondrial, 3781 bp) and (ii) in the chemical composition of male marking secretions (MMS), a key trait for mate attraction in bumblebees, by gas chromatography-mass spectrometry (GC-MS). Our results provide evidence for genetic differentiation in Corsican bumblebees and show that, contrary to theoretical expectations, island populations of bumblebees exhibit levels of genetic variation similar to the mainland populations. Likewise, our comparative chemical analyses of MMS indicate that Corsican populations of bumblebees are significantly differentiated from the mainland yet they hold comparative levels of within-population MMS variability compared to the mainland. Therefore, insularity has led Corsican populations to diverge both genetically and chemically from their mainland relatives, presumably through genetic drift, but without a decrease of genetic diversity in island populations. We hypothesize that MMS divergence in Corsican bumblebees was driven by a persistent lack of gene flow with mainland populations and reinforced by the preference of Corsican females for sympatric (Corsican) MMS. The impoverished Corsican bumblebee fauna has not led to relaxation of stabilizing selection on MMS but to consistent differentiation chemical reproductive traits on the island.
Common human reproductive inefficiencies have multiple etiologies. Going against chance, many effects, such as polycystic ovaries, endometriosis, and folate metabolic issues, have genetic components, while aneuploid losses arise from diverse mitotic and meiotic errors at different stages, some transitory. This can be advantageous, since greater overall survival with fewer offspring can increase reproductive success. Benefits primarily accrue to mothers, who bear most child related costs, and for whom early losses are less costly than late. Different adaptations to different situations reflect human evolutionary history. For early speciation, periodic climate extremes repeatedly reduced resources, favoring limitations while contracted populations helped fix relevant genes. Later, under better conditions, evolving social cooperation could increase fecundity faster than it added resources, further supporting reproductive suppression through mitotic aneuploidy, with very early losses minimizing maternal costs. The grandmother hypothesis suggests benefits in limiting reproduction as maternal age increased pregnancy risks in order to support grandchildren as they arrived, selecting for maternal age-related meiotic aneuploidy. Finally, with variable short-term agricultural shortages, acute reproductive responses arose through chromatin nutrient sensor-regulated epigenetic effects that also shifted some lethal effects earlier, reducing both maternal and mutation load costs. Overall, despite suggestions to the contrary, it is likely that human selective pressures have not decreased with civilization, but that many of the costs have been shifted to early reproduction.
Abstract Genes involved in sexual reproduction diverge rapidly as a result of reproductive fitness. Here, we identify a novel protein domain in the germline-specific Polycomb protein SCML2 that is required for the establishment of unique gene expression programs after the mitosis-to-meiosis transition in spermatogenesis. We term this novel domain, which is comprised of rapidly evolved, DNA-binding repeat units of 28 amino acids, the SCML2 DNA-binding (SDB) repeats. These repeats are acquired in a specific subgroup of the rodent lineage, having been subjected to positive selection in the course of evolution. Mouse SCML2 has two DNA-binding domains: one is the SDB repeats and the other is an RNA-binding region, which is conserved in human SCML2. For the recruitment of SCML2 to target loci, the SDB repeats cooperate with the other functional domains of SCML2 to bind chromatin. The cooperative action of these domains enables SCML2 to sense DNA hypomethylation in an in vivo chromatin environment, thereby enabling SCML2 to bind to hypomethylated chromatin. We propose that the rapid evolution of SCML2 is due to reproductive adaptation, which has promoted species-specific gene expression programs in spermatogenesis. Here, we identify a novel protein domain in the germline-specific Polycomb protein SCML2; because the domain is comprised of rapidly evolved DNA-binding repeats, it has been termed the SCML2 DNA-binding (SDB) repeats.
Distant hybridization can combine together the genomes of different species, which leads to changes of the offspring in phenotypes and genotypes. In this study, we successfully establish a fertile hybrid lineage by intergeneric hybridization of female blunt snout bream (BSB, Megalobrama amblycephala) x male topmouth culter (TC, Culter alburnus) and investigate some important biological traits of this lineage including the morphological traits, chromosomal number, karyotype, DNA content, gonadal development, egg and milt yield, sperm shape and density, fertilization rate and early survival rate. The results show that: (1) the diploid and triploid hybrids coexist in F-1 and only diploid hybrids are found in F-2, in which the diploid hybrids of F-1 and F-2 possess 48 chromosomes with one chromosome set of BSB and one chromosome set of TC, and the triploid hybrids of F-1 possess 72 chromosomes with two chromosome sets of BSB and one chromosome set of TC. (2) All the tested males and females of the diploid F-1 and F-2 hybrids have the normal gonadal development and produce mature sperm and egg, respectively, which are fertilized with each other to form F-2 and F-3 hybrids, respectively, and finally form a diploid hybrid lineage (F-1-F-3). (3) The good fertility of the F-1 and F-2 hybrids of female BSB x male TC potentially provides reproductive base to make the hybrid lineage propagate from one generation to another. The formation of the hybrid lineage (F-1-F-3) also provides an ideal model to research the reproductive rules of distant hybrid progeny. (C) 2014 Elsevier B.V. All rights reserved.
• Premise of the study: The mating system is an important component of the complex set of reproductive isolation barriers causing plant speciation. However, empirical evidence showing that the mating system may promote reproductive isolation in co‐occurring species is limited. The mechanisms by which the mating system can act as a reproductive isolation barrier are also largely unknown. • Methods: Here we studied progeny arrays genotyped with microsatellites and patterns of stigma–anther separation (herkogamy) to understand the role of mating system shifts in promoting reproductive isolation between two hybridizing taxa with porous genomes, Pitcairnia albiflos and P. staminea (Bromeliaceae). • Key results: In P. staminea, we detected increased selfing and reduced herkogamy in one sympatric relative to two allopatric populations, consistent with mating system shifts in sympatry acting to maintain the species integrity of P. staminea when in contact with P. albiflos. • Conclusions: Mating system variation is a result of several factors acting simultaneously in these populations. We report mating system shifts as one possible reproductive barrier between these species, acting in addition to numerous other prezygotic (i.e., flower phenology and pollination syndromes) and postzygotic barriers (Bateson–Dobzhansky–Muller genetic incompatibilities).