The dry-forest population in Morelos
Martínez-Peralta and Martínez-Zavala studied Coryphantha elephantidens near Quilamula in the state of Morelos in central Mexico. Observations of floral biology and pollination were made in 2016–2018. The two sites were about 1,5 km apart in a landscape of tropical dry forest and secondary vegetation. The results presented here apply to this population and the material studied. [Martínez-Peralta and Martínez-Zavala 2021, pp. 103–105]
Flowers opened during the day and closed at night. Of the 20 flowers followed, 40% functioned for one day and 60% for two days. Opening was widest in the afternoon. In bisexual flowers, pollen was available on the first day, while the stigma became receptive the next day. This temporal separation is protandry. The stigma was also positioned above the anthers within the flower. [Martínez-Peralta and Martínez-Zavala 2021, pp. 104–107, Sections 2.2, 3.1]
Female and bisexual flowers
The population contained pollen-producing flowers and functionally female flowers. In the latter, visible stamens had smooth anthers without pollen. In a sample of 119 flowers from 2016–2018, 37% were female. This proportion describes the flowers observed. In 11 plants with several flowers open at once, all flowers on a given individual were of the same sex. The authors described the system as gynodioecy, the coexistence of bisexual and female individuals. [Martínez-Peralta and Martínez-Zavala 2021, pp. 105–108, Fig. 4]
A search for nectar in 25 flowers in August 2018 found none. The main recorded reward for bees remained pollen, available only in bisexual flowers. Visits to female flowers may therefore result from similarity of appearance or other signals. In the studies described, similarity as a cause of visits was considered a hypothesis, without experimental separation of the individual signals. [Martínez-Peralta and Martínez-Zavala 2021, pp. 105–107, 110–111]
Self-incompatibility and cross-pollination
In the 2016 experiment, 27 flowers were self-pollinated and none set fruit. Another 27 were pollinated with a mixture of pollen from five other plants. Of this group, 63% set fruit. In a sample of 27 flowers left for open pollination, fruit set was 70%. The probability of fruit set and the number of seeds in fruits did not differ significantly between cross-pollination and open pollination. [Martínez-Peralta and Martínez-Zavala 2021, pp. 104–105, 108–109, Section 3.2]
The result supports the identification of self-incompatibility in the material studied. Self-pollen did not produce a fruit even when placed on the stigma by hand. The similar outcome of crossing and natural pollination indicates that, under the conditions of this experiment, insects supplied pollen that enabled reproduction. Temporal separation of floral functions does not remove the need to receive compatible pollen from another plant. [Martínez-Peralta and Martínez-Zavala 2021, pp. 108–111]
Visits to flowers of both sexes
A subsequent study used recordings from August 2018. They covered 48 plants and 52 flowers, 26 of each sex. Total recording time was 944 minutes. There were 2388 recorded bee visits, including 1789 to bisexual flowers and 599 to female flowers. Visit frequency was calculated per minute because individual recordings differed in length. [Martínez-Peralta et al. 2024, pp. 1113–1115]
Mean frequency was 3,58 ± 3,20 visits per minute for bisexual flowers and 1,21 ± 1,03 for female flowers. Dispersion was reported as the standard deviation. Augochlorini, a group of small metallic-coloured bees, were recorded most often. The species identified were also established using insects collected in August 2019. Those collections served for identification, while visit frequencies were calculated from the earlier videos. [Martínez-Peralta et al. 2024, pp. 1113–1115, Table 2, Fig. 2]
Contact with the stigma
Augochlorini concentrated on the stamens and pollen collection, touching the stigma relatively rarely. Ashmeadiella opuntiae, a bee specialized in using cactus flowers, often landed directly on the stigma. It visited flowers of both sexes, and the absence of a clear preference between them favours the possibility of pollen transfer to female flowers. Females of this insect contacted reproductive structures more often, while much of the males' behaviour involved seeking a mate. [Martínez-Peralta et al. 2024, pp. 1115–1120, Fig. 3–4]
The honeybee Apis mellifera was recorded only in bisexual flowers. It often touched the stamens before the stigma. The authors considered that this movement might increase deposition of the flower's own pollen, which is ineffective in a self-incompatible plant. Recorded behaviour identifies a likely route of pollen transfer. The contribution of individual bees to pollination nevertheless remains an assessment based on visits and contacts. Neither the number of grains delivered to a stigma nor fruit set following a single visit by each species was measured. [Martínez-Peralta et al. 2024, pp. 1116–1121]
Flower biology of the cactus Coryphantha elephantidens in the tropical dry forest of Central Mexico
Martínez-Peralta C., Martínez-Zavala A., Flower biology of the cactus Coryphantha elephantidens in the tropical dry forest of Central Mexico, Plant Species Biology, 2021, 36(1):102-113, doi: 10.1111/1442-1984.12303
Flower biology and the breeding system of Coryphantha elephantidens in the dry tropical forest of Morelos. It combines phenology, flower measurements, pollen presence, self-pollination, cross-pollination and bee observations. It documents functionally female flowers, protandry, herkogamy and dependence of fruit set on cross pollen in the population studied.
Bee species perform differently between sexes of a gynodioecious globose cactus
Martínez-Peralta C., Palma-Bahena A., Arroyo-Cosultchi G., Fierros-López H. E., Bee species perform differently between sexes of a gynodioecious globose cactus, Arthropod-Plant Interactions, 2024, 18(5):1111-1122, doi: 10.1007/s11829-024-10101-5
An analysis of recordings of bees visiting female and hermaphroditic flowers of Coryphantha elephantidens. It compares visit frequency and duration, and insect contact with the stigma and anthers. It discusses the behaviour of native bees and the honeybee, and the potential significance of visits for pollen transfer.