The role of phenotypic plasticity and pollination environment in the cleistogamous, mixed mating breeding system of Triodanis perfoliata.

The role of variable pollination environments in maintaining mixed mating systems is an active area of research. Dimorphic cleistogamy, in which a plant reproduces by both open, facultative outcrossing chasmogamous (CH) flowers and closed, cleistogamous (CL) flowers presents an excellent opportunity to study mixed mating. For example, plastic responses in allocation to an optimal floral type could serve as an adaptive strategy that maintains mixed mating under variable pollination environments. We tested for pollen limitation and plastic responses in allocation to different floral types under manipulated pollination conditions in the dimorphic cleistogamous, mixed mating annual, Triodanis perfoliata. Using a field population, we quantified pollen limitation, auto-fertility and plastic responses in the breeding system by measuring allocation to flower number and seed set of floral types. We found no evidence for pollen limitation for CH flowers, and CH flowers had low efficacy of autonomous selfing. Importantly, we found that T. perfoliata alters floral number following changes in pollination conditions, with pollen-supplemented plants having lower relative CH flower number than non-supplemented plants. Breeding system plasticity may allow for benefits from outcrossing through CH flowers, but also increased overall fitness through relatively cheap CL reproduction. After CH flowers receive pollen, subsequent production of CH flowers was reduced, which may be due to resource limitation. Our findings did not support a theoretical model predicting increased CH flowers with high pollination levels. These results increase our understanding of the role of pollination services and resource allocation in the maintenance of mixed mating systems, which also warrants further investigation.

Variation in heterostylous breeding systems in neighbouring populations of Oxalis alpina (Oxalidaceae).

UNLABELLED: The heterostylous reproductive system of Oxalis alpina in the Galiuro Mts. of Arizona was investigated using field surveys, controlled crosses in the greenhouse and measurements of reproductive morphs. Although populations in the Pinaleño Mts. to the immediate east and in the Santa Catalina Mts. to the immediate west have derived distylous reproductive systems, tristyly, the ancestral reproductive system in O. alpina, has been retained in the Galiuro Mts. POPULATION: Tristylous incompatibility relationships in the Galiuro population are modified from the ancestral condition, with significant loss of incompatibility differentiation between stamen whorls of both short- and long-styled morphs. Morphological adjustments of anther positions in the Galiuro population of O. alpina match those expected in light of incompatibility modification, with divergence of the mid-level anthers away from the position of the mid stigmas of the mid-styled morph. The occurrence of tristyly in an area of Arizona where distyly is found in adjacent mountain ranges is particularly remarkable, and indicates both the isolation of populations restricted to the upper elevations of these mountain ranges and variation in the tempo of evolution over short geographic distances.

Broadband spectrum generation using continuous-wave Raman scattering.

We experimentally demonstrate a continuous-wave ro-vibrational Raman spectrum that is two octaves wide with spectral components ranging from 0.8 to 3.2 µm in wavelength. The spectrum is produced in low pressure molecular deuterium inside a high finesse cavity.

Variation in floral longevity in the genus Leptosiphon: mating system consequences.

Pollination or fertilisation trigger floral senescence in a wide range of flowering plants, and yet little attention has been given to the implications of this phenomenon to mating system evolution. We examined the effects of pollination on floral senescence in the genus Leptosiphon. Species in the genus exhibit a wide range of breeding systems. In all cases, compatible pollination induced senescence; emasculated flowers lived longer than hand-outcrossed flowers. In the self-compatible species, Leptosiphon acicularis and L. bicolor, and in one highly selfing population of L. jepsonii, unmanipulated flowers had reduced longevity compared to emasculated flowers, suggesting that autonomous self-pollination limits floral longevity in these species. Limited floral longevity in these highly selfing taxa may reduce opportunities for male outcross success, representing a possible source of selection on the mating system. In turn, the mating system might influence how selection acts on floral longevity; obligately outcrossing taxa are expected to benefit from longer floral longevities to maximise opportunities for pollination, while selfing taxa might benefit from earlier floral senescence to reduce resource expenditure. Overall, the longevity of unpollinated flowers increased with the level of outcrossing in the genus Leptosiphon. Our results taken together with those of a previous study and similar results in other species suggest that floral longevity may represent a largely unexamined role in mating system evolution.

Tunable source of terahertz radiation using molecular modulation.

We describe a source of terahertz (THz) radiation that is based on Raman down-shifting of an infrared laser beam using highly coherent molecular vibrations. The source can operate in either the pulsed or the continuous wave (CW) regime and is tunable over much of the THz region of the spectrum (1-10 THz). In the pulsed regime, we predict average output powers of order 10 mW and peak powers approaching 1 MW. In the CW regime, average powers exceeding 100 µW with spectral linewidths at the hertz level are achievable.

Continuous-wave, multiple-order rotational Raman generation in molecular deuterium.

We demonstrate the generation of ≈10 rotational sidebands using continuous-wave stimulated Raman scattering in molecular deuterium. The generation occurs inside a high-finesse cavity at molecular gas pressures of ≈0.1 atm.