ASYMMETRIC EFFECTS OF LOSS AND GAIN OF A FLORAL TRAIT ON POLLINATOR PREFERENCE

Shifts in pollination syndromes involve coordinated changes in multiple floral traits. This raises the question of how plants can cope with rapid changes in pollinator availability by the slow process of accumulation of mutations in multiple genes. Here we study the transition from bee to hawkmoth pollination in the genus Petunia. Interspecific crosses followed by single locus introgressions were used to recreate putative intermediate evolutionary stages in the evolution of moth pollination. The effect of the loss/gain of petal color was asymmetric: it had no influence on the established pollinator but enhanced visitation by the new pollinator. Therefore, shifts in pollination syndromes may proceed through intermediate stages of reduced specialization and consequently enhanced reproductive assurance. The loss of petal color in moth‐pollinated Petunia involves null mutations in a single regulatory gene, An2. Such simple genetic changes may be sufficiently rapid and frequent to ensure survival during pollinator failure.     

Cytokinin induces the developmentally restricted synthesis of an extracellular protein in Physcomitrella patens

Early development of the moss Physcomitrella patens follows a simple course leading to the formation of a filamentous protonema containing only two cell-types, chloronema and caulonema. The addition of the hormone cytokinin leads to the induction of multicellular buds from such protonema. The spectrum of extracellular proteins (ECPs) synthesized by P. patens has been investigated at defined stages of development and under defined hormone treatments. It is found that in contrast to the limited changes in intracellular protein synthesis detectable, in the extracellular environment major and specific changes in the patterns of proteins synthesized occur. For example, the presence of caulonema cells is characterized by the synthesis of a 25 kDa ECP whereas early chloronema differentiation is distinguished by the presence of a 38 kDa ECP. The analysis of the pattern of ECPs synthesized by developmental mutants altered in bud formation, and in response to cytokinin in tunicamycin treated protonema (in which bud induction is blocked) indicate that the synthesis of a 14 kDa ECP is specifically induced by cytokinin. This protein represents a novel cytokinin-induced ECP. These data show that the differentiation of particular cell types in plants is associated with the synthesis of particular ECPs, and suggest that hormones which induce specific morphogenic events may do so via the synthesis of specific ECPs.     

Differential responses of tissue viscance and collateral resistance to histamine and leukotriene C4

Alterations in tissue viscance (Vti) and collateral resistance (Rcoll) are both used as indexes of peripheral lung responses. However, it is not known whether the two responses reflect the effects of activation of the same contractile elements. We measured differential responses in Vti and Rcoll to histamine and leukotriene (LT) C4 to determine whether each evoked a similar pattern of response. Using the wedged bronchoscope constant-flow technique, we measured Rcoll in lobar segments of anesthetized, paralyzed, open-chest, mechanically ventilated mongrel dogs. In addition, we measured (with an alveolar capsule) alveolar pressure (PA) within the segment under study. This allowed us to calculate Vti, the component of the PA change in phase with segment flow. Rcoll and Vti measurements were obtained under base-line conditions and after local delivery of aerosols generated from histamine and LTC4. In five out of five lobes studied with both histamine and LTC4, the fractional Rcoll response to histamine was greater than the fractional Rcoll response to LTC4. In contrast, in four out of five lobes examined, the fractional increase in Vti accompanying the histamine response was less than the fractional increase in Vti accompanying LTC4 administration. These data suggest that anatomically distinct contractile elements influence Vti and Rcoll insofar as LTC4 and histamine evoke quantitatively different changes in these two indexes of peripheral lung responses.     

Using hybrid systems to explore the evolution of tolerance to damage

Hybridization is common and important to the adaptive evolution of plants. Hybridization has resulted in the formation of new species and the introgression of traits between species. This paper discusses the advantages of using hybrid systems to explore the evolution of tolerance to herbivore damage (i.e., the ability to diminish the negative effects of damage on fitness). The major consequence of hybridization likely to make it influential for tolerance evolution is that hybridization generates broad variation in traits that can be selected for or against. In addition to generating greater variation in tolerance to damage and its putative traits (e.g., traits associated with allocation patterns and meristem production), hybridization can generate greater independence among tolerance traits and between tolerance and defense traits. Greater independence may provide a greater ability to discern mechanisms of tolerance, give a greater probability of detecting allocation costs of tolerance, and provide an effective means to evaluate tradeoffs between tolerance and defense. Interspecific hybrid systems can also be used to evaluate the importance of co-adaptation of tolerance traits. Moreover, recombinant hybrids can be used in selection studies focusing on tolerance to damage to discern whether parental combinations of tolerance traits are favored over novel combinations. Research in hybrid systems that investigate the selective importance of tolerance, the patterns of inheritance of tolerance traits, and the genetic architecture of plant species involved can be vital to our evaluation of the adaptive role of tolerance to damage. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of endogenous prostaglandins on acetylcholine release from dog trachealis muscle

We used a radioenzymatic technique to measure effects of the prostaglandin synthesis inhibitor indomethacin and of exogenous prostaglandin E2 (PGE2) and prostaglandin I2 (PGI2) on acetylcholine (ACh) efflux from canine tracheal smooth muscle (TSM) during sustained electrical field stimulation (EFS; 2 Hz, 2 ms pulse duration, 50 V for 15 min). ACh efflux from indomethacin (INDO, 10(-6) M)-pretreated and control TSM increased with consecutive stimulations. However, efflux of ACh was greater in INDO-treated than control muscles. INDO increased the tension produced by TSM in response to EFS. Neither PGE2 (10(-8) M) nor PGI2 (10(-6) M) had any effect on ACh efflux from INDO-pretreated TSM during the first of three periods of EFS. However, PGI2 and PGE2 prevented the progressive increase in ACh efflux observed on subsequent stimulations. PGE2 but not PGI2 decreased contractions of TSM caused by EFS. Our results demonstrate that endogenous prostaglandins, probably PGE2, do inhibit EFS-evoked ACh release from canine TSM in vitro, but suggest that these prostaglandins modulate EFS-evoked contractions predominantly by postsynaptic mechanisms.     

Characterization of 26 microsatellite marker loci in the fossa (Cryptoprocta ferox)

The fossa (Cryptoprocta ferox) is one of eight carnivore species endemic to Madagascar. This species lives in the forests of Madagascar and is classified as vulnerable by the IUCN due to the loss and fragmentation of its natural habitat and the hunting pressure of local people. Twenty-six nuclear microsatellite loci were isolated from genomic DNA derived from a free-ranging fossa from Betampona, Madagascar. Population genetic parameters were estimated on 28 individuals from nine European zoos establishing a baseline to study the genetic health and diversity of captive fossas to support the European Breeding and Conservation Program (EEP). The marker suite averaged 4.4 alleles per locus with an average polymorphic information content of 0.478.