Selective pollination by fungus gnats potentially functions as an alternative reproductive isolation among fiveArisaemaspecies

Abstract

Background and Aims Interspecific difference in pollinators (pollinator isolation) is important for reproductive isolation in flowering plants. Species-specific pollination by fungus gnats has been discovered in several plant taxa, suggesting that they can contribute to reproductive isolation. Nevertheless, their contribution has not been studied in detail, partly because they are too small for field observations during flower visitation. To quantify their flower visitation, we used the genus Arisaema (Araceae) because the pitcher-like spathe of Arisaema can trap all floral visitors. Methods We evaluated floral visitor assemblage in an altitudinal gradient including five Arisaema species. We also examined interspecific differences in altitudinal distribution (geographic isolation) and flowering phenology (phenological isolation). To exclude the effect of interspecific differences in altitudinal distribution on floral visitor assemblage, we established 10 experimental plots including the five Arisaema species on high- and low-altitude areas and collected floral visitors. We also collected floral visitors in three additional sites. Finally, we estimated the strength and contribution of these three reproductive barriers using the unified formula for reproductive isolation. Key Results Each Arisaema species selectively attracted different fungus gnats in the altitudinal gradient, experimental plots, and additional sites. Altitudinal distribution and flowering phenology differed among the five Arisaema species, whereas the strength of geographic and phenological isolations were distinctly weaker than those in pollinator isolation. Nevertheless, the absolute contribution of pollinator isolation to total reproductive isolation was weaker than geographic and phenological isolations, because pollinator isolation functions after the two early-acting barriers in plant life history. Conclusions Our results suggest that selective pollination by fungus gnats potentially contributes to reproductive isolation. Since geographic and phenological isolations can be disrupted by habitat disturbance and interannual climate change, the strong and stable pollinator isolation might compensate for the weakened early-acting barriers as an alternative reproductive isolation among the five Arisaema species.

Fly Pollination of Kettle Trap Flowers of Riocreuxia torulosa (Ceropegieae-Anisotominae): A Generalized System of Floral Deception

“…It is not known whether Ditassa flowers are deceptive. Representatives of deceptive and pollinator-trapping plant species in other families, such as Aristolochiaceae ( Aristolochia ; [ 25 , 26 , 27 ]), Araceae ( Arisaema ; [ 28 , 29 , 30 , 31 , 32 ]), and orchids (e.g., Pleurothallis [ 33 ], Trichosalpinx [ 34 ], Lepanthes [ 35 ], Pterostylis [ 36 , 37 ]) are likewise known to be visited/pollinated by Phoridae ( Megaselia ), Sciaridae ( B radysia , Corynoptera , Pseudolycoriella ), Chloropidae ( Oscinimorpha ), and Ceratopogonidae ( Forcipomyia ). Furthermore, various economically important crops (e.g., Cacao; [ 38 ]) depend on the same dipteran families and genera for pollination.…”

Arisaema: Pollination by lethal attraction

“…Indeed, even though artificial cross experiments have determined the cross-compatibility among species belonging to the Pistillata species (Murata et al, 2018), these Arisaema species often co-occur in apparent reproductive isolation. Pollinator specialization contributes to the reproductive isolation of these species (Kakishima et al, 2019;Kakishima et al, 2020;Matsumoto et al, 2019;Matsumoto et al, 2021;Suetsugu et al, 2021).…”

“…Indeed, even though artificial cross experiments have determined the cross‐compatibility among species belonging to the Pistillata species (Murata et al, 2018), these Arisaema species often co‐occur in apparent reproductive isolation. Pollinator specialization contributes to the reproductive isolation of these species (Kakishima et al, 2019; Kakishima et al, 2020; Matsumoto et al, 2019; Matsumoto et al, 2021; Suetsugu et al, 2021). For example, Suetsugu et al (2021) reported that the mycetophilid fungus gnats trapped by inflorescences of the sympatric, co‐blooming, and closely related species Arisaema angustatum and Arisaema peninsulae differed significantly.…”

“…Plants that mimic mushrooms, including the exceptional fungal mimetic Arisaema species ( A. sikokianum ), are visited by various fungivorous insects such as Mycodrosophila species (Drosophilidae) and staphylinids (Coleoptera; Kakishima et al, 2019; Matsumoto et al, 2019; Matsumoto et al, 2021). In contrast, many other Arisaema species (especially Pistillata taxa) are exclusively pollinated by a limited number of fungus gnat species (one or two) (Suetsugu et al, 2021).…”

Possible adaptive and non‐adaptive radiation in three plant genera in the Japanese archipelago

“…A maximum‐likelihood phylogenetic tree of 51 Pistillata species based on 2832 bp of four plastid DNA regions with pollination system characteristics and floral morphologies shown on the right only when information on pollination systems is available (OTUs highlighted in white circles in the phylogenetic tree). In the pie charts, green, yellow, purple, and gray slices indicate the relative frequencies of pollination by Mycetophilidae, Sciaridae, Drosophilidae, and other insects, respectively Source : Drawn based on Ohi‐Toma et al (2016), Kakishima et al (2019, 2020), Matsumoto et al (2019, 2021), Suetsugu et al (2021) [Color figure can be viewed at wileyonlinelibrary.com]…”