Resource allocation among sexual,clonal reproduction and vegetative growth of two Potamogeton species and their hybrid: Adaptability of the hybrid in relation to its parents

Resource allocation, as well as the tradeoffs among different reproductive components, plays an important role in the adaptability of plants to different environments. The hybrid may exhibit a higher adaptability in life history in heterogeneous environments because of the genetic variation derived from its parents. In this study, we exploited three levels of water depths and two types of sediments to investigate the resource allocation pattern of the first generation of the natural hybrid Potamogeton ×intortifolius compared to its parents P. wrightii and P. perfoliatus. We also measured the ramet survivorship and the seed set of the hybrid P. ×intortifolius. Our results showed that P. ×intortifolius had higher ramet survival than its parents at 1.5-m water depth on clay sediment. The possible tradeoffs showed that in P. ×intortifolius the tradeoff pattern between sexual and clonal reproduction was more pronounced in limiting environments. The individuals allocated more resources to sexual reproduction when the environment was limiting, which might confer a higher ability to utilize resources, to produce offspring and to found new populations. Although the seed set of P. ×intortifolius was lower than its parents, it had a higher ability to increase its seed set when the environment was limiting (sandy sediment) than its parents, which might benefit its future survival. These results indicated that the F₁ hybrid P. ×intortifolius was more able to adapt to limiting environments than one or both of its two parental taxa.     

Hologenomic speciation: synergy between a male‐killing bacterium and sex‐linkage creates a ‘magic trait’ in a butterfly hybrid zone

Danaus chrysippus (L.) in Africa comprises four substantially isolated semispecies that are migratory and hybridize on a seasonal basis throughout the eastern and central part of the continent. In the hybrid zone (but not elsewhere), the butterfly is commonly host to a male killing endosymbiotic bacterium, Spiroplasma sp., which principally infects one semispecies, Danaus chrysippus chrysippus in Kenya. A W‐autosome mutation, inherited strictly matrilinearly, links B and C colour gene loci, which have thus gained sex‐linkage in chrysippus. We have monitored variation in sex ratio and genotype at the A and C colour gene loci for two extended periods of 18 months (2004–5) and 12 months (2009–10) in adults reared from wild eggs laid on trap plants in Kasarani, near Nairobi, Kenya. Additionally, in 2009–10, all surviving adult butterflies were screened for Spiroplasma infection. The hybridizing Kasarani population is highly atypical in three respects, and has apparently been so for some 30 years: first, the sex ratio is permanently female‐biased (as expected), although subject to seasonal fluctuation, being lowest (male/female) when D. c. chrysippus (cc) peaks and highest when Danaus chrysippus dorippus (CC) predominates; second, the population is invariably dominated by Cc heterozygotes of both sexes but especially females; and third, cc males are always scarce because they are systematically eliminated by male killing, whereas the CC genotype is male‐biased. It is this imbalance of sex versus genotype that determines the massive departure from Hardy–Weinberg equilibrium in the population, in part because cc females have little choice but to pair with C‐ males. We suggest that: first, Cc hybrids of both sexes fail to disperse in the company of either parental semispecies; second, Spiroplasma positive females carrying the W‐autosome mutation have a selective advantage over females that lack the translocation; third, the endoparasite and the translocation create a ‘magic trait’ linkage group that underlies hologenomic reproductive isolation between two emerging species, D. c. chrysippus and D. c. dorippus; and, fourth, that the predominance of males in dorippus suggests that individuals must be protected by a male‐killing suppressor gene. By contrast to the C locus, Aa heterozygotes are in substantial and permanent deficit, suggesting either assortative mating between AA (chrysippus and dorippus) and aa (Danaus chrysippus alcippus), or heterozygote unfitness, or both. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 92–109.     

A long-term study on interactions between the Adh and αGpdh allozyme polymorphisms and the chromosomal inversion In(2L)t in a seminatural population of D. melanogaster

The Adh and αGpdh allozyme loci (both located on the second chromosome) showed considerable fluctuations in allele frequencies in a seminatural population of Drosophila melanogaster during 1972–97. Both long-term and short-term fluctuations were observed. The short-term fluctuations occurred within almost all years and comparison of allele frequencies between winters and summers showed significantly higher Adh^S (P < 0.001) and αGpdh^F (P < 0.01) allele frequencies in summers. Frequencies of these alleles were significantly positively correlated with environmental temperature, suggesting the adaptive significance of these allozyme polymorphisms. Frequency changes of the Odh locus (located on the third chromosome) showed no seasonal pattern and were not correlated with environmental temperature. Almost all short-term and long-term increases in Adh^S frequency were accompanied by a corresponding decrease in αGpdh^S frequency (r = –0.82, P < 0.001) and vice versa. Further analysis showed that gametic disequilibria between the Adh and αGpdh loci, which frequently occurred, were due to the presence of inversion In(2L)t located on the same chromosome arm and In(2L)t frequencies were positively correlated with environmental temperature. Gametic disequilibria between Adh and Odh and between Odh and αGpdh were hardly observed. Because In(2L)t is exclusively associated with the Adh^S/αGpdh^F allele combination, the observed correlated response in Adh/αGpdh allele frequencies is (at least partly) explained by hitchhiking effects with In(2L)t. This means that the adaptive value of the allozyme polymorphisms has been overestimated by ignoring In(2L)t polymorphism. Fluctuations in Adh allele frequencies are fully explained by selection on In(2L)t polymorphism, whereas we have shown that αGpdh frequency fluctuations are only partly explained by chromosomal hitchhiking, indicating the presence of selective differences among αGpdh genotypes in relation with temperature and independent of In(2L)t. Frequency fluctuations of αGpdh and In(2L)t are consistent with their latitudinal distributions, assuming that temperature is the main environmental factor varying with latitude that causes directly or indirectly these frequency distributions. However, the results of the tropical greenhouse population show no correlation of Adh (independent of In(2L)t) and Odh allele frequencies with environmental temperature, which may indicate that the latitudinal distribution in allele frequencies for these loci is not the result of selection on the F/S polymorphism in a direct way.     

Contrasting responses to Pleistocene climate changes: a case study of two sister species Allium cyathophorum and A. spicata (Amaryllidaceae) distributed in the eastern and western Qinghai–Tibet Plateau

It has been hypothesized that species occurring in the eastern and the western Qinghai–Tibet Plateau (QTP) responded differently to climate changes during the Pleistocene. Here, we test this hypothesis by phylogeographic analysis of two sister species, Allium cyathophorum and A. spicata. We sequenced two chloroplast DNA (cpDNA) fragments (accD‐psaI and the rpl16 intron) of 150 individuals, and the nuclear (ITS) region of 114 individuals, from 19 populations throughout the distributional ranges of these species. The divergence between the two species was dated at 779 ‐ 714 thousand years before the present and was likely initiated by the most major glaciation in the QTP. Analysis of chlorotype diversity showed that A. spicata, the species occurring in the western QTP, contains much lower genetic diversity (0.25) than A. cyathophorum (0.93), which is distributed in the eastern QTP. Moreover, multiple independent tests suggested that the A. spicata population had expanded recently, while no such expansion was detected in A. cyathophorum, indicating a contrasting pattern of responses to Pleistocene climate changes. These findings highlight the importance of geographical topography in determining how species responded to the climate changes that took place in the QTP during the Pleistocene.