Plant species variation in bottom‐up effects across three trophic levels: a test of traits and mechanisms

1. An increasing number of studies have addressed the mechanisms by which plant inter‐specific variation influence interactions at higher trophic levels, but little is known about the underlying plant traits driving these dynamics. 2. Here we investigated the effects of host plant species on herbivore‐parasitoid interactions and the underlying traits driving such effects. For this, we measured the abundance of seed‐eating bruchids and their parasitoids across seven sympatric populations of the bean species Phaseolus coccineus and Phaseolus vulgaris in Central Mexico. To investigate the mechanisms underlying differences between bean species in bruchid‐parasitoid interactions, we carried out two laboratory experiments to test whether bruchid and parasitoid performance differed between plant species. We also measured seed size and phenolic compounds to investigate if seed traits mediate bruchid‐parasitoid interactions by influencing herbivore susceptibility or resistance to parasitoids. 3. Field surveys revealed that the rate of parasitoid recruitment to bruchids was significantly higher on P. vulgaris than on P. coccineus. Subsequent laboratory bioassays indicated that bruchids developed more slowly and exhibited lower fitness on P. vulgaris seeds than on P. coccineus seeds. Accordingly, we found that bean species differed in seed size, with P. vulgaris having smaller (less nutritious) seeds, which explains why bruchid development was slower on this plant species. 4. These results provide a mechanism for why bruchids exhibited higher parasitism rates on seeds of P. vulgaris in the field which could be due to Slow‐Growth/High‐Mortality effects, a smaller physical refuge provided by the seed, or both factors. The roles of these mechanisms remain inconclusive without further study.     

The Transpacific Origin of Mesoamerican Civilization: A Preliminary Review of the Evidence and Its Theoretical Implications

Anthropologists generally assume that civilization developed independently in the eastern and western hemispheres. Review of the features that distinguish the Olmec culture of Mesoamerica from preceding village farming groups shows, however, that many are present in the earlier Shang civilization of China. If Olmec civilization originated from a transpacific stimulus, this has important implications both for reconstruction of New World cultural development and for formulation of a valid theory of the evolution of civilization.     

Ecological distribution and niche segregation of sibling species: the case of bean beetles, Acanthoscelides obtectus Say and A. obvelatus Bridwell

Abstract.  1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure.
2.  Acanthoscelides obtectus and A. obvelatus are two sister species of bean bruchids, which have been confused until the last decade. One important ecological difference between them has emerged, however: A. obtectus is multivoltine and now distributed worldwide, whereas A. obvelatus is univoltine and restricted to Mesoamerica. Where their ranges overlap, the two species share the same host plants and larvae can sometimes complete development in the same seed.
3. The analysis of 27 622 Mexican individuals of the two species in 2001-2002 and 2002-2003 indicates that their niches overlap, but are differentiated with respect to altitude and the kind of beans (wild vs. domesticated). The principal patterns in their relative abundance in different habitats, and at different seasons, were constant from one year to the next.
4. As sympatry of these species seems to be of recent origin, the observed niche differentiation may not have evolved in response to competition, but could instead be the consequence of physiological differences, evolved independently in each species in allopatry, that pre-adapted them for different altitudes and kinds of resources.
5. The combination of biological and historical factors thus appears to allow these two sibling species to coexist in sympatry, despite their broadly overlapping ecological niches.     

Fine Structure of Haemoproteus columbae Kruse During Differentiation of the Ookinete*

Ookinete differentiation begins in vitro～1 hr after blood infected with mature gametocytes of Haemoproteus columbae is withdrawn from a pigeon. In the undifferentiated zygote, dense material accumulates at the point under the plasma membrane. The conoid and conoidal rings condense from this material. The nucleus is drawn out to a point with the intranuclear spindle (INS) at the peak. Atypical centrioles lie under the forming conoid in the cytoplasm next to the INS. Fibrous material under the inner membrane forms the polar ring from which subpellicular microtubules originate. One hr later the centrioles have disappeared and the nucleus has returned to the center of the organism. The conoidal complex forms the tip of a growing cytoplasmic projection, the anterior end of the ookinete. During this time an elaborate pellicle is differentiating antero-posteriorly; crystalloid formation begins with an extensive proliferation of rough endoplasmic reticulum (ER) continuous with the outer membrane of the nuclear envelope. Crystalloid particles are formed between the lamellae of the ER and collected in a sphere that is later partially surrounded by a small amount of ER. Ookinetes, differentiated 2 hr longer than the ookinetes in vitro, were obtained from the gut of the pigeon fly, Pseudolynchia maura. The differentiated pellicle of these ookinetes consists of a plasma membrane, an inner membrane layer composed of 2 appressed membranes, and in the anterior end, an electron-opaque lamina immediately under the inner membrane. Anterior to the polar ring, this lamina forms a canopy which, posteriorly, is drawn out into projecting ribs which diminish and disappear in the first third of the organism. Fifty to 60 subpellicular microtubules insert on the polar ring. Ookinetes differentiated in vitro were no more than 4 hr old. They lacked micronemes and retained a pellicular cytostome and “internal cytostomes.” The differentiation of micronemes probably occurs at a later time because they are visible after 6 hr in ookinetes in the fly gut. So many degenerating organisms appeared in vitro after 5 hr that this material was discarded.     

Aggregation facilitates larval growth in the neotropical nymphalid butterfly Chlosyne janais

1. Larvae of Chlosyne janais (Lepidoptera: Nymphalidae) feed gregariously as early instars on the shrub Odontonema callistachyum (Acanthaceae). During the fourth instar, aggregations break up and larvae feed as solitary individuals.
2. The hypothesis that aggregation increases growth rate was tested by raising larvae on intact plants in the field in different group sizes and measuring their daily growth.
3. There was a striking effect of group size on larval growth whereby larvae more than doubled their weight gain by feeding in large rather than small aggregations on intact plants in the field.
4. This group-feeding advantage was lost altogether if larvae were raised on excised leaves in the laboratory, suggesting that large aggregations may facilitate growth either by inducing a nutrient sink or by overwhelming an induced allelochemical response in the plant.
5. Although larval survival was higher in cages that excluded enemies than in exposed aggregations, there was no influence of group size (experimentally manipulated) on short-term survival in the field. However, there was a weak positive relationship between short-term survival and the size of naturally occurring larval aggregations in the field. These data provide mixed support for the notion that gregarious feeding promotes defence against natural enemies.
6. Although the group defence hypothesis warrants further investigation, feeding facilitation is clearly an important factor contributing to the aggregation behaviour of C. janais larvae.