Mitosis, stature and evolution of plant mating systems: low-Phi and high-Phi plants

There is a long-recognized association in plants between small stature and selfing, and large stature and outcrossing. Inbreeding depression is central to several hypotheses for this association, but differences in the evolutionary dynamics of inbreeding depression associated with differences in stature are rarely considered. Here, we propose and test the Phi model of plant mating system evolution, which assumes that the per-generation mutation rate of a plant is a function of the number of mitoses (Phi) that occur from zygote to gamete, and predicts fundamental differences between low-Phi (small-statured) and high-Phi (large-statured) plants in the outcomes of the joint evolution of outcrossing rate and inbreeding depression. Using a large dataset of published population genetic studies of angiosperms and conifers, we compute fitted values of inbreeding depression and deleterious mutation rates for small- and large-statured plants. Consistent with our Phi model, we find that populations of small-statured plants exhibit a range of mating systems, significantly lower mutation rates, and intermediate inbreeding depression, while large-statured plants exhibit very high mutation rates and the maximum inbreeding depression of unity. These results indicate that (i) inbred progeny typically observed in large-statured plant populations are completely lost prior to maturity in nearly all populations; (ii) evolutionary shifts from outcrossing to selfing are generally not possible in large-statured species, rather, large-statured species are more likely to evolve mating systems that avoid selfing such as self-incompatibility and dioecy; (iii) destabilization of the mating system-high selfing rate with high-inbreeding depression-might be a common occurrence in large-statured species; and (iv) large-statured species in fragmented populations might be at higher risk of extinction than previously thought. Our results help to unify and simplify a large and diverse field of research, and serve to emphasize the importance that developmental and genetic constraints play in the evolution of plant mating systems.     

Human fertility variation, size-related obstetrical performance and the evolution of sexual stature dimorphism

In several animal species, change in sexual size dimorphism is a correlated response to selection on fecundity. In humans, different hypotheses have been proposed to explain the variation of sexual dimorphism in stature, but no consensus has yet emerged. In this paper, we evaluate from a theoretical and an empirical point of view the hypothesis that the extent of sexual dimorphism in human populations results from the interaction between fertility and size-related obstetric complications. We first developed an optimal evolutionary model based on extensive simulations and then we performed a comparative analysis for a total set of 38 countries worldwide. Our optimization modelling shows that size-related mortality factors do indeed have the potential to affect the extent of sexual stature dimorphism. Comparative analysis using generalized linear modelling supports the idea that maternal death caused by deliveries and complications of pregnancy (a variable known to be size related) could be a key determinant explaining variation in sexual stature dimorphism across populations. We discuss our results in relation to other hypotheses on the evolution of sexual stature dimorphism in humans.     

Human size evolution: no evolutionary allometric relationship between male and female stature

In many animal groups, sexual size dimorphism tends to be more pronounced in species with large body size. Similarly, in a previous cross-cultural analysis, male and female stature in humans were shown to be positively allometrically related, indicating a similar relationship where populations with larger stature were more dimorphic. In this study, we re-examine the hypothesis of an allometric relationship between the sexes using phylogenetic methodology. First, however, we tested whether there exist phylogenetic signals in male and female stature. Data on mean stature from 124 human populations was gathered from the literature. A phylogenetic test showed that male and female stature were significantly associated with phylogeny. These results indicate that comparative methods that to some degree incorporate genetic relatedness between populations are crucial when analyzing human size evolution in a cross-cultural context. Further, neither non-phylogenetic nor phylogenetic analyses revealed any allometric relationship between male and female stature. Thus, we found no support for the idea that sexual dimorphism increases with increasing stature in humans.     

Femur/stature ratio and estimates of stature in children.

The present study examines the relationship between femur length and stature in children between the ages of 8 and 18 years. In previous investigations, my colleagues and I reported the surprising finding that femur length bears a nearly constant relationship to stature in adult humans regardless of ethnicity or gender. This earlier study revealed that the femur/stature ratio averages 26.74% in adult humans, and that using the ratio to predict stature from femur length yields remarkably accurate estimates. The current study shows that femur/stature ratios of children between the ages of 8 and 11 differ significantly from their older counterparts. Between the ages of 12 and 18, there are no significant differences due to age in the femur/stature ratio; however, there are significant differences in this age group attributable to gender. This study also shows that the worldwide average adult femur/stature ratio does not adequately describe children in this age range. This study strongly documents the adolescent growth spurt in the femur/stature ratios of both males and females at the precise time one would expect to see the spurt occur (10-12 in females; 12-14 in males). This growth follows a nearly identical trajectory in both genders, with relative femur growth dominating before the peak years of the growth spurt, and relative stature growth dominating afterward. This accounts for the ratio's rise to maximum values just before peak growth, and its decline toward the adult ratio thereafter. These findings require us to use separate adolescent femur/stature ratios of 27.16 (females) and 27.44 (males) to estimate the stature of children between the ages of 12 and 18. Preliminary testing shows these ratios to be more accurate in estimating stature than the properly selected Trotter and Gleser adult regression equation. Use of the adolescent male ratio with the Homo erectus juvenile WT 15000 results in a lower stature estimate (157.4 cm) than previously reported. It is suggested that continued testing of the ratio occur, but that the values herein derived may be useful in routine forensic cases involving children in this age range, and with subadult paleontological specimens.     

Gingival fibromatosis, short stature, border-line IQ, facial dysmorphism and hepatomegaly

Gingival fibromatosis, short stature, border-line IQ, facial dysmorphism and hepatomegaly: Gingival fibromatosis is a rare and benign disorder. The enlarged gingivae are firm and may interfere with speech, closure of the lips, and mastication. We report a thirteen years old girl, with gingival fibromatosis referred to the periodontics clinics. Full mouth gingivectomy and gingivoplasty were performed. Medical investigation showed short stature, low-borderline IQ, facial dysmorphism, and hepatomegaly. Histological analysis revealed hyperplasia in the epithelial area and fibrotic appearance of gingival connective tissue with dense collagen fibre clusters. Pedigree analysis confirmed that mode of inheritance is autosomal recessive. According to the combination of clinical findings, this case report may represent a previously unreported syndrome.     

Biomechanics of fruits and vegetables

The scope of fruit and vegetable biomechanics is reviewed. Sources of mechanical injury to produce in harvesting, processing, storage, packaging and transportation are briefly described. A survey of produce handling and transportation environments was conducted, whereby an envelope model encompassing composite spectra of trucks, railroad, marine and cargo aircraft is presented. The protective quality, i.e. strength of shipping containers is quantified in static and dynamic loading such as encountered in storage, handling and transportation. Mechanical response of fruits and vegetables in quasistatic and dynamic loading are formulated by a nonlinear rheological model, whereby a time and deformation dependent relaxation modulus is defined. A realistic link is established between the model and real fruits and vegetables by test procedures for determination of the parameters in the governing nonlinear equations. Based on the nonlinear relaxation modulus, mechanical damage of fruits and vegetables is quantified for static compression, transients and vibration loading as well as for combined static and dynamic loading, by equations of contact circle diameter, bruise depth and contact pressure. Distribution of loads over a maximal number of contact points per fruit is linked to geometrical patterns of produce packs. The application of Shock Damage Boundary techniques for produce-package testing is described along with a case study comparing the protective qualities of two types of apple packs. Produce damage quantification by direct fruit inspection in terms of a 'Bruise Index' is described, including a practical example, comparing the protective qualities of three types of apple packs in shipping tests. Indirect methods of mechanical injury evaluation, based on weight loss and CO2 emission differences between bruised and wholesome fruits are also briefly discussed.     

Femur/stature ratio and estimates of stature in mid- and late-Pleistocene fossil hominids

In previous limited investigations of the human femur/stature ratio we (Feldesman and Lundy: Journal of Human Evolution 17:583-596, 1988; Feldesman et al.: American Journal of Physical Anthropology 79:219-220, 1989) have shown it to be remarkably stable across ethnic and gender boundaries. In this study we evaluate the femur/stature ratio in 51 different "populations" of contemporary humans (n = 13,149) sampled from all over the world. We find that the mean ratio of femur length to stature in these populations is 26.74%, with a very restricted range of variation. When we compare mean femur/stature ratios of males and females, there are no statistically significant differences. ANOVA performed on a naive grouping of samples into "whites," "blacks," and "Asians" indicates that there are significant racial differences (P less than 0.001). When we subject these groups to Tukey's HSD procedure (a post-hoc test), we find that "blacks" are responsible for the significant ANOVA, being significantly (P less than 0.005) different from the other ethnic groups. "Whites" and "Asians" are not significantly different (P = 0.067) under the conditions of this analysis, although all these racial comparisons may be suspect given the small sample sizes. We tested the efficacy of the ratio in three situations: predicting stature of repatriated white Vietnam veterans; predicting stature in a random sample of South African blacks (of known stature), and predicting the stature of a single Akka pygmy. In the first and third cases, the femur/stature ratio does better than the traditionally recommended regression equation, while in the second case the predictions from the femur/stature ratio are less accurate than from the appropriate regression equation. These results encouraged us to apply this ratio to mid- and late-Pleistocene fossil hominids, where the choice of reference population for stature estimates continues to trouble workers. We estimated stature for a sizeable number of Homo erectus (HE), early Neanderthal (EN), Near Eastern Neanderthal (NEN), and early anatomically modern Homo sapiens (EAMHS) by using the simple relationship: stature (cm) = femur length (cm) * 100/26.74. Our results show that HE fossils are slightly taller on average than either EN or NEN samples, which do not differ significantly in stature, while EAMHS fossils are significantly taller than all three earlier groups. While these results are not surprising, our stature estimates for these fossils differ from currently published estimates based on sample-specific regression-based formulae.(ABSTRACT TRUNCATED AT 400 WORDS)