Mistletoe fruit‐colour polymorphism and differential success in a habitat mosaic

Abstract Polymorphisms in fruit colour are common in nature, but mechanistic explanations for the factor(s) responsible for their maintenance are for the most part lacking. Past studies have focused on frugivore colour preferences and fruit removal rates, but until recently there has been no evidence that these factors are responsible for the maintenance of the polymorphisms. For other types of genetic polymorphisms, habitat heterogeneity has been shown to play a role in their maintenance. Here we test the habitat heterogeneity hypothesis for a polymorphic New Zealand mistletoe. We show that red‐fruited and orange‐fruited morphs of the mistletoe Alepis flavida (Hook. F) Tiegh. (Loranthaceae) differ in their growth, mortality and flowering on forest edges and in forest interior. Red‐fruited morphs, which are preferred by dispersers, grew, survived and flowered as well as orange‐fruited morphs on edges, whereas orange‐fruited morphs had much greater growth, survival, and flowering than red‐fruited morphs in the forest interior. This is the first evidence that habitat‐specific differences in growth and survival may contribute to maintaining fruit‐colour polymorphisms.     

The effect of resistant solanaceous plants on the sex ratio of Heterodera rostochiensis and the use of the sex ratio to assess the frequency and genetic constitution of pathotypes

The sex ratios of two Heterodera rostochiensis populations were compared on fifteen solanaceous plants. Larvae did not mature in the roots of Atropa belladona, Datura stramonium or Nicotiana tabacum but adults were produced on the other plants, on some only males and on others, males and females. With two other populations, but not with a third, the percentage of larvae that became female on a potato hybrid with a dominant gene for resistance derived from Solanum tuberosum ssp. andigena increased during successive generations on the hybrid in accordance with the hypothesis that such larvae are double recessives (aa). Fewer larvae became adult in plants with two dominant genes for resistance than in plants with one, and such plants probably exerted selection of both males and females. A population from St Brelades (Jersey) produced fewer females and more males on the susceptible variety Arran Banner than did either the Thorney (Cambs.) or Aberystwyth populations. A much greater percentage of larvae from the St Brelades population became female on an ex andigena hybrid derived from CPC 1690 than on one derived from CPC 1685.     

The Effects of Seasonal Flooding on Seed Availability for Spring Migrating Waterfowl

Abstract: We hypothesized the seed biomass available to migrating waterfowl would be higher in spring- versus fall-flooded wetlands. To test this hypothesis we conducted an experiment using 5 pairs of wetland impoundments in northern Missouri, USA (2000-2002). We strategically assigned one impoundment of each pair to either a fall or spring treatment group. We estimated seed biomass in fall and in spring by clipping seed heads and collecting soil cores at 20 random locations within each impoundment. We placed exclosures near each fall sample site in spring-flooded impoundments to estimate seed loss from granivorous birds and rodents. Despite similar biomass in fall between treatments (P = 0.64), overwinter seed loss was greater in fall-flooded (79%; 1,324 ± 195 kg/ha) than in spring-flooded (31%; 653 6 130 kg/ha) impoundments (P = 0.009). Considering barnyard grass or millet (Echinochloa spp.) only, seed loss was higher in fall-flooded than in spring-flooded impoundments (P = 0.05). Spring biomass estimates were similar inside versus outside exclosures (P = 0.63) indicating loss to granivorous birds and rodents was limited. Our results suggest that fall flooding reduces seed availability for spring migrating waterfowl. We recommend spring flooding be used in areas where impoundment water levels can be manipulated to increase seed availability for spring migrating waterfowl.     

The population genetics of the potato cyst-nematode, Heterodera rostochiensis: mathematical models to simulate the effects of growing eelworm -resistant potatoes bred from Solatium tuberosum ssp. andigena

To follow population changes when potato varieties with resistance to Heterodera rostochiensis derived from Solanum tuberosum ssp. andigena were grown on infested land, a computer programme was written including three mathematical relationships: (1) a law relating multiplication to pre-cropping density; (2) two mathematical models of inheritance of ability to overcome resistance; (3) a law relating the proportion of larvae able to become female to pre-cropping population density. The programme also included four parameters: (1) the maximum possible reproductive rate; (2) the fraction of the population (eggs) not participating in reproduction when potatoes are grown and carried over to the following year unchanged; (3) the fraction carried over annually when other crops are grown; (4) the frequency of larvae able to become female in the population initially. Population density was measured relative to the equilibrium density and was therefore independent of the units in which density is usually measured. After supplying a range of parameters for all the above to include those likely to be encountered in practice, the changes expected (a) in the frequency of larvae able to become female in the roots of resistant varieties and (b) in population density were computed for resistant varieties grown continuously or alternately with susceptible varieties in crop rotations of different lengths. Because well established field populations are relatively dense, observed reproductive rates are small and rarely approach the maximum possible. Reproductive rate is therefore a relatively unimportant determinant of genetic change. The fraction of the population carried over to the following year is more important because it affects the length of a crop rotation necessary to make loss of potato yield acceptable, determines what the multiplication rate will be and influences the speed of genetic change by providing a reservoir of initial type males which backcross with any genetically different females that may develop on the roots of resistant plants. No experiment seems to have been done specifically to determine the parameters needed to calculate population changes. Some values can be obtained from the literature but mostly they must be guessed. When the law relating the proportion of larvae able to become female to pre-cropping population density was included in the computations, it had little effect initially but later, after several generations, it delayed genetic change. Two field experiments, one by Huijsman (1961) another by Williams (1958) and Cole & Howard (1962 a), provide some of the variables needed to compute trends in population density. Best fitting variables were computed for the data in these experiments by the method of maximum likelihood. The computed parameters for one experiment were not very realistic but those for the other were in line with what would be expected in practice and tended to favour the hypothesis that larvae able to become female in the roots of resistant plants are double recessives (aa). The computations lead us to suggest that the best policy for potato growers who have fields suitable for resistant varieties is to alternate resistant with susceptible varieties in a crop rotation containing potatoes every 3 or 4 years.     

Centennial‐scale changes to the aquatic vegetation structure of a shallow eutrophic lake and implications for restoration

1. We investigate long‐term (>200 years) changes to the composition and spatial structure of macrophyte communities in a shallow, eutrophic lake (Barton Broad, eastern England) and consider the implications for lake restoration. 2. Historical macrophyte data were assembled from a variety of sources: existing plant databases, museum herbaria, journal articles, old photographs and eyewitness accounts. Additionally, two types of sediment core sample were analysed for plant macro‐remains and pollen; bulk basal samples from multiple core sites analysed to provide information on ‘pre‐disturbance’ macrophyte communities and two whole cores analysed to determine historical change. 3. Prior to the late 1800s, macrophyte communities were diverse and included a multilayered mosaic of short‐stature submerged taxa and taller submerged and floating‐leaved species. With the progression of eutrophication after around 1900, the former community was displaced by the latter. Diversity was maintained, however, since an encroaching Schoenoplectus–nymphaeid swamp generated extensive patches of low‐energy habitat affording refugia for several macrophytes otherwise unable to withstand the hydraulic forces associated with open water conditions. When this swamp vegetation disappeared in the 1950s, many of the ‘dependent’ aquatic macrophytes also declined leaving behind a sparse, species‐poor community (as today) resilient to both eutrophication and turbulent open waters. 4. The combination of historical and palaeolimnological data sources offers considerable benefits for reconstructing past changes to the aquatic vegetation of lakes and for setting restoration goals. In this respect, our study suggests that successful restoration might often be better judged by reinstatement of the characteristic structure of plant communities than the fine detail of species lists; when nutrients are low and the structure is right, the right species will follow.     

Hybrid queen butterflies from the cross Danaus chrysippus (L.) × D. gilippus (Cramer):confirmation of species status for the parents and further support for Haldane's Rule

A cross between queen butterflies of the Palaeotropical species Danaus chrysippus and the Neotropical D. gilippus was achieved with difficulty in both directions. Only one progeny ( N  = 70) was reared comprising sterile males and inviable females in a precisely 1 : 1 ratio. Both prezygotic and postzygotic barriers to gene flow are strong. The result supports Haldane's Rule, to which we propose a minor amendment. The F₁ hybrids were intermediate for background colour between the brown (genotype BB ) of gilippus and orange (genotype bb ) of chrysippus . Most F₁ pattern characters were also intermediate. In polymorphic chrysippus populations, because Bb heterozygotes are brown, or nearly so, we suggest the B allele may have evolved towards dominance in sympatry. Hybrid males show positive heterosis for body size. The close similarity of male genitalia between the allopatric, genetically distant species chrysippus  and gilippus , compared to their divergence between gilippus and its largely sympatric sister species eresimus , suggest that reinforcement of sexual isolation or reproductive character displacement have evolved in sympatry.  © 2002 The Linnean Societyof London, Biological Journal of the Linnean Society , 2002, 76 , 535–544.     

Iophenoxic Acid as a Long-Term Marker for Wild Boar

ABSTRACT Chemical markers are increasingly used to investigate consumption of baits used to deliver vaccines, toxicants, and contraceptives. We evaluated whether ethyl-iophenoxic acid (Et-IPA) and propyl-iophenoxic acid (Pr-IPA) can be used as long-lasting systemic bait markers for wild boar (Sus scrofa). We presented captive wild boar with baits treated with either Et-IPA or Pr-IPA at 5 mg/kg (low dose), 10 mg/kg (medium dose), and 20 mg/kg (high dose) of body weight. We collected serum from each boar at 5 time points: 5 days, 3 weeks, 6 weeks, 11 weeks, and 39 weeks following ingestion of iophenoxic acid-treated baits. We detected both Et-IPA and Pr-IPA for ≥39 weeks after ingestion. Throughout the trial, the Et-IPA we found in serum was proportional to the amount eaten. At each time point, animals in the high-dose group had significantly more Et-IPA than animals in the low-dose group. We concluded that both compounds can be used as long-lasting markers in wild boar and that Et-IPA can also be employed as quantitative marker to indicate multiple bait uptake. Both compounds have potential applications in the context of vaccination, fertility, and population control campaigns, where baits are used to deliver pharmaceuticals, and in behavioral studies to establish spatial and temporal patterns of bait uptake.     

The butterfly Danaus chrysippus (L.) in East Africa comprises polyphyletic, sympatric lineages that are, despite behavioural isolation, driven to hybridization by female-biased sex ratios

Mitochondrial and nuclear DNA information was analysed among four subspecies of the African Queen butterfly, Danaus (Anosia) chrysippus sensu lato (s.l.), along with four other Danaus species drawn from all three subgenera (D. (Danaus) plexippus, D. (Salatura) genutia, D. (A.) gilippus, D. (A.) eresimus) and two outgroup species from the same tribe, Tirumala septentrionis and Amauris niavius. A mitochondrial phylogeny derived from the 12S rRNA (347 bp) and COI (537 bp) loci indicates two very distinct haplotypes for subspecies D. (A.) c. dorippus, dorippus‐1 and dorippus‐2. Interestingly, dorippus‐1, on the one hand, and all other D. (A.) chrysippus haplotypes, on the other, are the most distantly related clades within the genus and have different most recent ancestors from different subgenera, though sharing the common ancestor of the monophyletic genus. A phylogeny based on the EF1‐α nuclear locus (400 bp) shows that the two well‐separated mitochondrial lineages of dorippus are identical for this gene and reciprocally monophyletic to the other D. (A.) chrysippus lineages. Thus, nuclear and cytoplasmic phylogenies are not only discordant, but also suggest that both D. (A.) chrysippus s.l. and subspecies dorippus are polyphyletic. Paradoxically, four African subspecies, chrysippus‐orange, chrysippus‐brown, alcippus and dorippus, though substantially vicariant, hybridize extensively in East Africa wherever the ranges of two or more of them overlap. Linkage disequilibrium, and hence sexual isolation, in sympatry between colour (nuclear) genes and unlinked mitochondrial (cytoplasmic) loci is consistent across populations and therefore indicates the operation of positive natural selection. Together with data from previous experimental and field work, our results suggest that extensive hybridization occurs among once allopatric or parapatric lineages, that are now nascent species. We deduce that hybridism among lineages in sympatry is currently enforced, in the face of assortative mate choice, by a bacterial symbiont, Spiroplasma, a male‐killer that forces females in female‐biased populations to pair with heterotypic males. In discussion we emphasize that neither D. (A.) chrysippus s.l. as presently circumscribed, nor its component clades, conform to any established concept of species. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 117–131.