Comparative anatomy of the nectary spur in selected species of Aeridinae (Orchidaceae)

Background and Aims

To date, the structure of the nectary spur of Aeridinae has not been studied in detail, and data relating to the nectaries of ornithophilous orchids remain scarce. The present paper compares the structural organization of the floral nectary in a range of Aeridinae species, including both entomophilous and ornithophilous taxa.

Methods

Nectary spurs of Ascocentrum ampullaceum (Roxb.) Schltr. var. aurantiacum Pradhan, A. curvifolium (Lindl.) Schltr., A. garayi Christenson, Papilionanthe vandarum (Rchb.f.) Garay, Schoenorchis gemmata (Lindl.) J.J. Sm., Sedirea japonica (Rchb.f.) Garay & H.R. Sweet and Stereochilus dalatensis (Guillaumin) Garay were examined by means of light microscopy, scanning electron microscopy and transmission electron microscopy.

Key Results and Conclusions

The diverse anatomy of the nectary is described for a range of Aeridinae species. All species of Ascocentrum investigated displayed features characteristic of ornithophilous taxa. They have weakly zygomorphic, scentless, red or orange flowers, display diurnal anthesis, possess cryptic anther caps and produce nectar that is secluded in a relatively massive nectary spur. Unicellular, secretory hairs line the lumen at the middle part of the spur. Generally, however, with the exception of Papilionanthe vandarum, the nectary spurs of all entomophilous species studied here (Schoenorchis gemmata, Sedirea japonica, Stereochilus dalatensis) lack secretory trichomes. Moreover, collenchymatous secretory tissue, present only in the nectary spur of Asiatic Ascocentrum species, closely resembles that found in nectaries of certain Neotropical species that are hummingbird-pollinated and assigned to subtribes Maxillariinae Benth., Laeliinae Benth. and Oncidiinae Benth. This similarity in anatomical organization of the nectary, regardless of geographical distribution and phylogeny, indicates convergence.     

Fly pollination and duodichogamy in Bridelia stipularis and Cleistanthus sumatranus (Phyllanthaceae)

The globally distributed family Phyllanthaceae comprises 1745 species, all of which produce unisexual flowers, and most of the species occur in the tropics. The few species in which the pollination system has been studied are pollinated by flies, wasps, or specialized moths, and at least two species are duodichogamous. Here we report on the flowering phenology and pollination of the Chinese species Bridelia stipularis and Cleistanthus sumatranus, which were studied on the tropical Hainan Island. Both species are duodichogamous and indicated to be fly‐pollinated. The calliphorid species Chrysomya megacephala, Isomyia isomyia, Pierretia sp., Hemipyrellia sp., and Achoetandrus tufifacies were the most frequent flower visitors to B. stipularis; some of these species together with syrphids (Meliscaeva cinctella, Dideopsis sp., and Eristalis sp.) were the most abundant visitors to Cl. sumatranus flowers. Fruit set in hand‐pollinated flowers was higher than in open‐pollinated flowers, but because of natural fruit abortion the difference was not significant, indicating that fly pollinators do not limit reproduction of these Phyllanthaceae species. This study provides an addition to the limited Asian literature on pollination by flies and the even more limited literature on duodichogamy. It could help to broaden our understanding for analysis of the evolution of duodichogamy in future research, but the specific ecological factors behind the evolution of this rare sexual system are still difficult to generalize.     

A field evaluation of the sexual competitiveness of sterile melon flies, Dacus (Zeugodacus) cucurbitae

ABSTRACT.

• 1 The sexual competitiveness of sterile melon fly males [Ducus (Zeugodacus) cucurbitue Coquillett] was estimated under field conditions.
• 2 The value of competitiveness was about 0.8 for flies in the fifth to tenth generation from the beginning of mass-rearing, but decreased to about 0.2 in the eighteenth generation.
• 3 The sexual competitiveness estimated using laboratory data was near unity even in the final stage of our study.
• 4 It was concluded that the field evaluation of sexual competitiveness is essential to determine the quality of the insects reared for purposes of pest control.

     

Comparative floral biology of Rhynchospora ciliata (Vahl) Kukenth and R. pubera (Vahl) Boeckeler (Cyperaceae): the role of white involucral bracts in attracting pollinating insects

Although Cyperaceae are considered anemophilous, some species exhibit features that are attractive to pollinators, such as the white UV‐reflecting involucral bracts of Rhynchospora ciliata. But how effective are these conspicuous adaptations? To address this question, we tested the hypothesis that species such as R. ciliata are visited by greater numbers of pollinating insects than similar species with green involucral bracts, such as R. pubera. We compared the floral biology of both species and the number of visits to sympatric populations of each species, associating them with the availability of pollen and the pollination system. We verified that species with white involucral bracts are preferred, because there were more visits to R. ciliata in the first 2 h the flowers were open. The peak visitation in R. pubera was 2 h after the flowers opened, when the pollen of R. ciliata was exhausted. Although the involucral bracts of R. pubera are green, the spikelet scales and anthers are white and reflect ultraviolet light. Overall, flowers of R. pubera exhibit fewer white or reflective surfaces and are probably less conspicuous to a bee than those of R. ciliata. It is possible that R. pubera is a second option for visitors after the first 2 h of anthesis. The two different peaks in visitation minimize interspecific competition for pollinators, suggesting that R. ciliata and R. pubera together could attract more generalist pollinators and, instead of competing, facilitate the pollination of both species. Although R. pubera is autogamous and self‐compatible, both wind and insects are important to its reproductive success.     

Moonlight pollination in the gymnosperm Ephedra (Gnetales)

Most gymnosperms are wind-pollinated, but some are insect-pollinated, and in Ephedra (Gnetales), both wind pollination and insect pollination occur. Little is, however, known about mechanisms and evolution of pollination syndromes in gymnosperms. Based on four seasons of field studies, we show an unexpected correlation between pollination and the phases of the moon in one of our studied species, Ephedra foeminea. It is pollinated by dipterans and lepidopterans, most of them nocturnal, and its pollination coincides with the full moon of July. This may be adaptive in two ways. Many nocturnal insects navigate using the moon. Further, the spectacular reflection of the full-moonlight in the pollination drops is the only apparent means of nocturnal attraction of insects in these plants. In the sympatric but wind-pollinated Ephedra distachya, pollination is not correlated to the full moon but occurs at approximately the same dates every year. The lunar correlation has probably been lost in most species of Ephedra subsequent an evolutionary shift to wind pollination in the clade. When the services of insects are no longer needed for successful pollination, the adaptive value of correlating pollination with the full moon is lost, and conceivably also the trait.     

Male eyespan size is associated with meiotic drive in wild stalk-eyed flies (Teleopsis dalmanni)

This study provides the first direct evidence from wild populations of stalk-eyed fliesto support the hypothesis that male eyespan is a signal of meiotic drive. Severalstalk-eyed fly species are known to exhibit X-linked meiotic drive. A recent quantitativetrait locus analysis in Teleopsis dalmanni found a potential link betweenvariation in male eyespan, a sexually selected ornamental trait, and the presence ofmeiotic drive. This was based on laboratory populations subject to artificial selectionfor male eyespan. In this study, we examined the association between microsatellitemarkers and levels of sex ratio bias (meiotic drive) in 12 wild T. dalmannipopulations. We collected two data sets: (a) brood sex ratios of wild-caught males matedto standard laboratory females and (b) variation in a range of phenotypic traitsassociated with reproductive success of wild-caught males and females. In each case, wetyped individuals for eight X-linked microsatellite markers, including several thatpreviously were shown to be associated with male eyespan and meiotic drive. We found thatone microsatellite marker was very strongly associated with meiotic drive, whereas asecond showed a weaker association. We also found that, using both independent data sets,meiotic drive was strongly associated with male eyespan, with smaller eyespan males beingassociated with more female-biased broods. These results suggest that mate preference forexaggerated male eyespan allows females to avoid mating with males carrying the meioticdrive gene and is thus a potential mechanism for the maintenance and evolution of femalemate preference.     

Co-evolution of male and female reproductive characters across the Scathophagidae (Diptera)

Sperm morphometry is extremely variable across species, but a general adaptive explanation for this diversity is lacking. As sperm must function within the female, variation in sperm form may be associated with variation in female reproductive tract morphology. We investigated this and other potential evolutionary associations between male and female reproductive characters across the Scathophagidae. Sperm length was positively associated with the length of the spermathecal (sperm store) ducts, indicating correlated evolution between the two. No association was found between sperm length and spermathecal size. However, the size of the spermathecae was positively associated with testis size indicating co-evolution between male investment in sperm production and female sperm storage capacity. Furthermore, species with a higher degree of polyandry (larger testes) had longer spermathecal ducts. However, no associations between sperm length or length variation and testis size were found which suggests greater sperm competition sensu stricto does not select for longer sperm.     

Effects of laboratory colonization on Bactrocera dorsalis (Diptera,Tephritidae) mating behaviour: ‘what a difference a year makes’

Laboratory-reared insects are widely known to have significantly reduced genetic diversity in comparison to wild populations; however, subtle behavioural changes between laboratory-adapted and wild or ‘wildish’ (i.e., within one or very few generations of field collected material) populations are less well understood. Quantifying alterations in behaviour, particularly sexual, in laboratory-adapted insects is important for mass-reared insects for use in pest management strategies, especially those that have a sterile insect technique component. We report subtle changes in sexual behaviour between ‘wildish’ Bactrocera dorsalis flies (F1 and F2) from central and southern Thailand and the same colonies 12 months later when at six generations from wild. Mating compatibility tests were undertaken under standardised semi-natural conditions, with number of homo/heterotypic couples and mating location in field cages analysed via compatibility indices. Central and southern populations of Bactrocera dorsalis displayed positive assortative mating in the 2010 trials but mated randomly in the 2011 trials. ‘Wildish’ southern Thailand males mated significantly earlier than central Thailand males in 2010; this difference was considerably reduced in 2011, yet homotypic couples from southern Thailand still formed significantly earlier than all other couple combinations. There was no significant difference in couple location in 2010; however, couple location significantly differed among pair types in 2011 with those involving southern Thailand females occurring significantly more often on the tree relative to those with central Thailand females. Relative participation also changed with time, with more southern Thailand females forming couples relative to central Thailand females in 2010; this difference was considerably decreased by 2011. These results reveal how subtle changes in sexual behaviour, as driven by laboratory rearing conditions, may significantly influence mating behaviour between laboratory-adapted and recently colonised tephritid fruit flies over a relatively short period of time.