Landscape management and domestication of Stenocereus pruinosus (Cactaceae) in the Tehuacan Valley: human guided selection and gene flow

ABSTRACT: BACKGROUND: Use of plant resources and ecosystems practiced by indigenous peoples of Mesoamerica commonly involves domestication of plant populations and landscapes. Our study analyzed interactions of coexisting wild and managed populations of the pitaya Stenocereus pruinosus, a columnar cactus used for its edible fruit occurring in natural forests, silviculturally managed in milpa agroforestry systems, and agriculturally managed in homegardens of the Tehuacan Valley, Mexico. We aimed at analyzing criteria of artificial selection and their consequences on phenotypic diversity and differentiation, as well as documenting management of propagules at landscape level and their possible contribution to gene flow among populations. METHODS: Semi-structured interviews were conducted to 83 households of the region to document perception of variation, criteria of artificial selection, and patterns of moving propagules among wild and managed populations. Morphological variation of trees from nine wild, silviculturally and agriculturally managed populations was analyzed for 37 characters through univariate and multivariate statistical methods. In addition, indexes of morphological diversity (MD) per population and phenotypic differentiation (PD) among populations were calculated using character states and frequencies. RESULTS: People recognized 15 pitaya varieties based on their pulp color, fruit size, form, flavor, and thorniness. On average, in wild populations we recorded one variety per population, in silviculturally managed populations 1.58 +/- 0.77 varieties per parcel, and in agriculturally managed populations 2.19 +/- 1.12 varieties per homegarden. Farmers select in favor of sweet flavor (71% of households interviewed) and pulp color (46%) mainly red, orange and yellow. Artificial selection is practiced in homegardens and 65% of people interviewed also do it in agroforestry systems. People obtain fruit and branches from different population types and move propagules from one another. Multivariate analyses showed morphological differentiation of wild and agriculturally managed populations, mainly due to differences in reproductive characters; however, the phenotypic differentiation indexes were relatively low among all populations studied. Morphological diversity of S. pruinosus (average MD = 0.600) is higher than in other columnar cacti species previously analyzed. CONCLUSIONS: Artificial selection in favor of high quality fruit promotes morphological variation and divergence because of the continual replacement of plant material propagated and introduction of propagules from other villages and regions. This process is counteracted by high gene flow influenced by natural factors (pollinators and seed dispersers) but also by human management (movement of propagules among populations), all of which determines relatively low phenotypic differentiation among populations. Conservation of genetic resources of S. pruinosus should be based on the traditional forms of germplasm management by local people.     

Spiral growth in the radially-expanding piloboloid mutants ofPhycomyces blakesleeanus

The growth zone of the sporangiophore of a piloboloid mutant,pil, ofPhycomyces expands radially at an increased rate until the growth zone becomes nearly spherical, in sharp contrast to that of the wild-type sporangiophore which exhibits longitudinal elongation only and is conical. The rotation of thepil sporangiophore reverses its direction from clockwise (CW) to counterclockwise (CCW) during the period of increased radial expansion, and the CCW rotation continues as long as does the radial expansion. The direction of rotation and the time of reversal are correlated with the relative rates of cell-wall expansion in the longitudinal and transverse directions. The CCW rotation of the sporangiophore of this mutant can be explained by the behavior of the microfibrils, as previously proposed to explain the rotation of the wild-type sporangiophore.Abbreviations CW clockwise - CCW counterclockwise — both as viewed from above     

A review of subspecies recognition in polydesmidan millipedes (Diplopoda) with a revision of the subspecies of Euryuridae (Xystodesmoidea)

Jorgensen, M. C., Sierwald, P. & Mason‐Gamer, R. J. (2012). A review of subspecies recognition in polydesmidan millipedes (Diplopoda) with a revision of the subspecies of Euryuridae (Xystodesmoidea). —Zoologica Scripta, 42, 317–326. Taxonomic subspecies recognition is controversial due to the lack of an objective definition of the concept and inconsistent use of the category. The practice of designating subspecies is assessed here through a thorough review of 244 subspecies designations of polydesmidan millipedes over a 50‐year period. The survey focuses on the justification given for subspecies recognition, the amount of data available for the designation, the handling of nominate subspecies and the criteria used for diagnosis. We address several problematic issues and provide suggestions to enhance future work. Three examples of subdivided species from the Euryuridae (Polydesmida) are presented in detail with some taxonomic revision. Euryurus leachii leachii and E. leachii fraternus are synonymized, and the subspecific epithets are discarded. Auturus erythropygos erythropygos and A. erythropygos becki are returned to full species rank.     

Internal ethnicity in the ethnic economy

Internal ethnicity refers to ethnic subgroups within an immigrant group. An ‘ethnic economy’ includes the self‐employed and their co‐ethnic workers. Although most research treats the boundaries of ‘ethnic economy’ and its variant, the ‘ethnic enclave economy’, as though they were coterminous with those of national‐origin immigrant groups, this assumption is unreliable. Ethnic boundaries need not coincide with those of nationality origin when internal ethnicity exists. To test this hypothesis, we utilize survey data collected from a sample of Iranians in Los Angeles. Because this national‐origin immigrant group contains four ethno‐religious subgroups (Armenians, Bahais, Jews and Muslims), the Iranians in Los Angeles operated four distinctive ethnic economies, not one. Each ethno‐religious subgroup had its own ethnic economy, and these separate economies were only weakly tied to an encompassing Iranian ethnic economy.     

Scale effects and constraints for sound production in katydids (Orthoptera: Tettigoniidae): correlated evolution between morphology and signal parameters

Male katydids (Orthoptera: Tettigoniidae) produce mating calls by rubbing the wings together, using specialized structures in their forewings (stridulatory file, scraper and mirror). A large proportion of species (ca. 66%) reported in the literature produces ultrasonic signals as principal output. Relationships among body size, generator structures and the acoustic parameters carrier frequency (f_c) and pulse duration (p_d), were studied in 58 tropical species that use pure‐tone signals. A comparative analysis, based on the only available katydid phylogeny, shows how changes in sound generator form are related to changes in f_c and p_d. Anatomical changes of the sound generator that might have been selected via f_c and p_d are mirror size, file length and number of file teeth. Selection for structures of the stridulatory apparatus that enhance wing mechanics via file‐teeth and scraper morphology was crucial in the evolution of ultrasonic signals in the family Tettigoniidae.     

Optimal climbing speed explains the evolution of extreme sexual size dimorphism in spiders

Several hypotheses have been put forward to explain the evolution of extreme sexual size dimorphism (SSD). Among them, the gravity hypothesis (GH) explains that extreme SSD has evolved in spiders because smaller males have a mating or survival advantage by climbing faster. However, few studies have supported this hypothesis thus far. Using a wide span of spider body sizes, we show that there is an optimal body size (7.4 mm) for climbing and that extreme SSD evolves only in spiders that: (1) live in high‐habitat patches and (2) in which females are larger than the optimal size. We report that the evidence for the GH across studies depends on whether the body size of individuals expands beyond the optimal climbing size. We also present an ad hoc biomechanical model that shows how the higher stride frequency of small animals predicts an optimal body size for climbing.     

Extrapair paternity in a flock-living passerine, the vinous-throated parrotbill Paradoxornis webbianus

Understanding the factors that affect the occurrence of extrapair paternity (EPP) is one of the central issues in sexual selection. We investigated genetic parentage and the ecological factors affecting patterns of EPP in the vinous-throated parrotbill, Paradoxornis webbianus , a flock-living species with double broods. Using microsatellite DNA fingerprinting, we determined parentage of 246 offspring in 50 broods over two years (2005 and 2006). Nineteen offspring (8%) from 13 broods (26%) were sired by extrapair males and one offspring (0.4%) was probably the result of intraspecific brood parasitism. The prevalence of EPP varied significantly through the breeding season: 95% of broods with EPP (12/13) occurred in the first of two laying peaks. Parentage assignment revealed that half of extrapair males (6/12) were adjacent neighbours. The distribution of EPP was not significantly related to the ecological factors including breeding density and breeding synchrony. Instead, we suggest that social characteristics such as flocking and weak territoriality may determine the observed pattern of EPP in this study.     

Chick growth rates in Charadriiformes: comparative analyses of breeding climate, development mode and parental care

The rate at which a young bird grows is highly diverse across taxa. We investigated the influences of ecological variables on growth rates of shorebirds, gulls and their allies (order Charadriiformes) using comparative analyses of 68 species. We investigated three hypotheses: (1) exposure to cold temperatures results in reduced growth rate due to the increased energy expenditure required for thermoregulation, (2) fast growth rates allow offspring to complete development in habitats with short periods of fair ecological conditions, and (3) parental feeding allows the offspring to grow faster than self-feeding offspring. Charadriiform species are suitable for testing these hypotheses, because they breed in diverse environmental conditions that include Arctic and Antarctic habitats, temperate zones and tropics, and in some species the offspring feed themselves (precocial) whereas in others they are fed by the parents (semi-precocial). First, we tested the influence of ambient temperature on growth rate and we found that species breeding in cold habitats had faster growth rates than species breeding in warm temperatures. The relationship between growth rate and ambient temperature was not significantly different between precocial and semi-precocial offspring. Second, we tested the influence of the length of the breeding season on growth rate, and we found that species with shorter breeding seasons had faster growth rates than species with longer breeding seasons. Finally, we show that precocial offspring grew slower than semi-precocial offspring, and this relationship remains significant when the influences of ambient temperature and breeding season length are statistically controlled. In conclusion, our work, using phylogenetically corrected models, confirms that ambient environment and developmental mode of young together influence the growth of Charadriiform chicks, and their effects are additive.