Effect of inbreeding on production of filled seed in Pinus radiata — experimental results and a model of gene action

Summary Pinus radiata D. Don was inbred to different degrees, commencing with a founder population of 8 clones. Yield of filled seed was determined for each mating type. Mean yields (%), relative to outcrossing, were: half-sib 102; full-sib 97; S₁ 43; S₂ 42. An epistatic model was developed to predict the empty seed yield following selfing, assuming that homozygosity for several recessive co-lethals is necessary to kill an embryo. Calculations were then extended to predict the yields following different degrees of inbreeding. The proposed model gave a better fit to present results, and to other published results of similar investigations, than did an alternative based on action of independent recessive lethals. Implications for breeding and seed production strategy are discussed.     

The impact of domestication on distribution of allozyme variation within and among cultivars of radish,Raphanus sativus L.

Summary Allozyme surveys of cultivated plant species generally report little within-cultivar variation, but considerable among-cultivar variation. This trend contrasts with natural plant populations in which most allozyme variation resides within, rather than among, populations. The difference may be an artifact of the extreme inbreeding techniques used to develop and propagate these crops, rather than a consequence of domestication per se. To test this hypothesis, we compared the population genetic structure of 24 lines of radish cultivars — a domesticated species developed and maintained as open-pollinated, outcrossed populations — with four wild radish populations in California. Although the wild populations displayed more overall allozyme variation than the cultivars, most of the allozyme variation in the cultivars remains partitioned within, rather than among, lines. Apparently, how a crop is developed and maintained can have a profound influence on the organization of genetic variation of that species.     

Selection of sites for egg deposition and spawning dynamics in the waccamaw darter

Synopsis We provided 93 experimental spawning covers for the waccamaw darter. We grouped the covers (3 sizes of slate and one of concave tile) in three arrangements at six Lake Waccamaw locations to separate the variables of water depth, distance from shore, cover density and cover type. Tag returns of marked males suggest low fidelity for nest sites. Egg production under the 3 different sizes of slate was not significantly different. Egg production under the tile was significantly less than that under the slates. Egg production was significantly higher off the undeveloped southeastern shore in 2 m of water and lowest at the shallowest location with the highest experimental cover density. The number of eggs in nest is positively correlated with male size. We conclude that medium size slate covers placed in a linear arrangement in 2 m of water on a mixed sand bottom result in the highest egg production for the waccamaw darter.     

Hour of delivery in cynomolgus monkeys under indoor individually-caged conditions

The hour of delivery was surveyed in 152 cynomolgus monkeys (Macaca fascicularis) which were kept in individual cages placed in completely air-conditioned and artificially lit rooms. The deliveries took place during light hours (05:00–19:00) in 15 animals (10%) and during dark hours (19:00–05:00) in 137 (90%). No significant differences in delivery hour were observed between animals of feral origin and colony-bred F1 animals. In addition, there was no difference according to gravidity.     

Prediction of ground reaction forces and moments during various activities of daily living

Inverse dynamics based simulations on musculoskeletal models is a commonly used method for the analysis of human movement. Due to inaccuracies in the kinematic and force plate data, and a mismatch between the model and the subject, the equations of motion are violated when solving the inverse dynamics problem. As a result, dynamic inconsistency will exist and lead to residual forces and moments. In this study, we present and evaluate a computational method to perform inverse dynamics-based simulations without force plates, which both improves the dynamic consistency as well as removes the model?s dependency on measured external forces. Using the equations of motion and a scaled musculoskeletal model, the ground reaction forces and moments (GRF&Ms) are derived from three-dimensional full-body motion. The method entails a dynamic contact model and optimization techniques to solve the indeterminacy problem during a double contact phase and, in contrast to previously proposed techniques, does not require training or empirical data. The method was applied to nine healthy subjects performing several Activities of Daily Living (ADLs) and evaluated with simultaneously measured force plate data. Except for the transverse ground reaction moment, no significant differences (P>0.05) were found between the mean predicted and measured GRF&Ms for almost all ADLs. The mean residual forces and moments, however, were significantly reduced (P>0.05) in almost all ADLs using our method compared to conventional inverse dynamic simulations. Hence, the proposed method may be used instead of raw force plate data in human movement analysis using inverse dynamics.     

Fruit‐breeding drosophilids (Diptera) in the Neotropics: playing the field and specialising in generalism?

1. Species of Drosophilidae are frequently used as model organisms, but their relationships with the environment, particularly in immature stages, remain poorly known. 2. This is the most comprehensive survey to date of fruit‐breeding drosophilids and their hosts in the Neotropics. Drosophilid host‐utilisation patterns were analysed as to geographic origin (native versus exotic) and level of specialisation. 3. The 180 species of plants recorded as drosophilid hosts are distributed across the main Angiosperm lineages and fleshy‐fruited orders; plant families that hosted the greatest number of drosophilid species were Arecaceae, Moraceae, and Myrtaceae. The 100 nominal drosophilid species recorded breeding in fruits belong to just over one‐third of Neotropical genera; most species (91) belong to Drosophila. Drosophilid species with the greatest resource breadth were Drosophila simulans, Drosophila nebulosa, and Zaprionus indianus. 4. Exotic drosophilids breed in more plant species than Neotropical drosophilids and use exotic hosts more frequently, possibly because they are generalists that have survived the trial of introduction and establishment in the Neotropics. Native drosophilids are more variable in resource breadth and sometimes adopt exotic hosts. 5. Amongst the 49 drosophilids with enough records for analysis (> 4), 48 were categorised as generalists. One possible explanation for such overwhelming generalism is the high diversity of Neotropical habitat or hosts. A second, non‐exclusive explanation, suggested by recent studies and empirically supported by the absence of host specialisation found in this study, is that drosophilids could be selective of the dominant yeasts and bacteria in host tissue, and not of the hosts themselves.     

Developmental studies in trebouxioid algae and taxonomical consequences

In the genusTrebouxia (incl.Pseudotrebouxia) two sorts of nonmotile reproductive cells exist: autospores and aplanospores. In subg.Trebouxia small mother cells give rise to 4, 8, or 16 autospores, while comparatively large mother cells develop into zoosporangia or, if the release of zoospores is arrested, into aplanosporangia. Both zoo- and aplanosporangia contain (32) 64 or 128 daughter cells. The transformation of trophic cells into zoo-/ aplanosporangia starts with the formation of a local thickening of the cell wall that marks the prospective opening, and (in most species) with the disappearance of the pyrenoids; sooner or later strong starch deposition can be observed. In subg.Eleutherococcus autospores do not occur; zoo- and aplanosporangia are formed essentially in the same way as in subg.Trebouxia. Differences occur between the form and position of chloroplasts during successive divisions: flattened and parietal in subg.Eleutherococcus, not flattened and ± central in subg.Trebouxia. InEleutherococcus, besides large cells also relatively small cells may produce zoo- or aplanospores.—Dictyosomes could be observed in the living state in representatives of subg.Eleutherococcus under optimal conditions. In trophic cells they are arranged in a group surrounding a hyaline area at the side of the nucleus. In young uninuclear sporangia they are positioned between the nucleus and the local thickening of the cell wall. In somewhat older sporangia they occupy mainly those parts of the nuclear surface which is turned towards the cytoplasmatic cleavage furrow. In subg.Trebouxia dictyosomes could not be observed by light-microscopy. In several species the chloroplast lobation (observed under optimal conditions) differs from that described in the literature.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday, together with cordial thanks for initial scientific guidance and fifty years of stimulation and encouragement.     

Reversed sexual size dimorphism in raptors: evaluation of the hypotheses in kestrels breeding in a temporally changing environment

Reversed sexual size dimorphism (RSD, females larger than males) is commonly found in birds of prey. We used kestrels (Falco tinnunculus), breeding in western Finland in a temporally varying environment of 3-year vole cycles, to assess current hypotheses for the evolution and maintenance of RSD. Our 12-year data showed only weak correlations between parental size and breeding parameters (laying date, clutch size and the number of fledglings produced). The degree of RSD per se was unrelated to breeding success, contrary to the prediction of the female dominance hypothesis. Females with small males produced larger clutches in low-vole years, independently of laying date, which supports the small male (or its equivalent inter-sexual selection) hypothesis. Small females tended to have more fledglings, particularly in low-vole years, which is inconsistent with the hypotheses for an advantage of large female size (the starvation, intra-sexual selection, reproductive effort, and supplementary feeding hypotheses). As for males, smaller females may be more efficient hunters, the importance of which should be most pronounced under harsh breeding conditions. Our results suggest that the directional selection on a particular size in kestrels may be under contrasting selection pressures by the environment, and, at least in breeding females, the advantages of large size can actually be counterbalanced during harsh environmental conditions. Received: 7 May 1999 / Accepted: 20 January 2000     

Systematics and evolutionary history of heavy metal tolerant Thlaspi caerulescens in Western Europe: evidence from genetic studies based on isozyme analysis

Thlaspi caerulescens is distributed in Europe on metalliferous and not metalliferous soils. Individuals from populations growing on heavy metal contaminated soils are well known as hyperaccumulators of zinc and cadmium. The taxonomical treatment of subspecies of Thlaspi caerulescens is unsettled. We investigated the degree of genetic variation among 28 populations of Thlaspi caerulescens from Europe with isozyme analysis to compare inter- and intrapopulational diversity. British material from heavy metal contaminated environments recognized as Thlaspi sylvestre and T. occitanicum are quite similar to each other on the level of isozyme polymophisms, but they are more closely related to populations from non-contaminated stands from Scandinavia and Middle Europe than to metallophytes distributed in Continental Europe. Our findings indicate that a taxonomical subdivision of T. caerulescens is not possible and, furthermore, heavy metal tolerance might have evolved twice in populations of Thlaspi caerulescens from different areas. The trait of zinc tolerance and hyperaccumulation is frequently found in numerous relatives of Thlaspi caerulescens, and it is suggested that this trait has been established and manifested in populations from metalliferous sites during postglacial colonization. From Scandinavia only non-metallophytes are known. These populations are very similar to each other on the isozyme level. This fits to the hypothesis that Thlaspi caerulescens was introduced to Scandinavia in recent times by human activity. Despite full self-compatibility we estimated varying outcrossing rates up to 0.88 in the metallophytes and 0.658 in the non-metallophytes depending on population size and structure.