Pollen interference between rare and common species
Data files
Oct 18, 2024 version files 225.53 KB
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PollenInterferenceRareAndCommonSpecies.txt
221.82 KB
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README.md
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Abstract
The mechanisms underlying plant species distribution and abundance have been long studied in ecology. However, the role of heterospecific pollen interference in shaping these patterns remains unaddressed. Species distribution and abundance are important factors determining whether a species is endangered or not, thus understanding the impact of heterospecific pollen interference on rare species could help to inform conservation strategies aimed at preserving plant communities.
In this study, we conducted a multispecies experiment using eight co-occurring and co-flowering plant species with varying rarity levels in Switzerland. We performed hand-pollination experiments between all species pairs and measured seed set (whether a flower produces seed) and seed number (number of seeds per flower) as outcomes. We looked at the effects of species rarity status, species self-compatibility and recipient-donor relatedness on heterospecific pollen interference.
Contrary to expectations, neither seed set nor seed number were affected by heterospecific pollen deposition. Self-compatible species had a higher seed set probability, but this was independent from species rarity. Lastly, rare species showed a decrease in heterospecific pollen interference with more distantly related pollen donors when these were rare as well. In our study setting, heterospecific pollen interference seems to have only minor effects on seed set and seed number, and consequently on recruitment. Thus, heterospecific pollen interference seems to play only a minor role in shaping plant species distribution and abundance. Nevertheless, the higher impact of heterospecific pollen deposition for rare and closely related species might need further investigation for both in-situ and ex-situ conservation strategies.
README
Data from multispecies greenhouse experiment where conspecific pollination and heterospecific pollination were performed between eight species with different rarity in Switzerland, to assess heterospecific pollen interference. All eight species belong to the habitat type "Caucalidion". Species were grown in the greenhouse from seeds collected in the wild and treated once they started to flower. Seeds produced were counted as outcome variable.
Treatments:
For the heterospecific pollen treatment, we prepared a saturated mix of conspecific pollen and heterospecific pollen and applied it to the stigma of the recipient flower. For each flower treated with heterospecific pollen mixture, we treated a second flower on the same plant individual on the same day with conspecific pollen only as a control, using the same conspecific pollen donor that we used for the heterospecific pollen mix. The two flowers with heterospecific and conspecific treatment would constitute a pair with the same “pair ID”. We standardized treatment by always applying a pollen amount above saturation level. We extracted the pollen for the treatments from the anthers by tapping them on a glass slide and with the help of tweezers, and then mixed it for the heterospecific treatment using tweezers. We then applied the pollen mixture (HP) or the conspecific pollen (CP) to the open stigma of the recipient flower. To avoid selfing, we emasculated recipient flowers by removing the anthers some days before treatment. For some species (Bupleurum rotundifolium, Fallopia convolvulus, Myosotis arvensis), anther removal would cause too much flower damage due to the small size, thus anthers were not removed. For these species, selfing could not be completely excluded.
For each donor-recipient combination, we treated between 2 and 16 flower pairs (HP and CP; median: 12 flower pairs per donor-recipient combination). We collected seeds after ripening, and counted them either by hand or by using an imaging method with imageJ (Abramoff, Magalhaes, & Ram, 2004)
Description of the data and file structure
# Recipient : Genus_species of the recipient; 8 species used (Ajuga_chamaepitys, Bupleurum_rotundifolium, Consolida_regalis, Fallopia_convolvulus, Iberis_amara, Myosotis_arvensis, Nigella_arvensis, Papaver_rhoeas,).
# Recipient.ID : ID of the plant individual of a given species.
# Flower.ID : ID of the flower within a plant individual.
# Type : Treatment type - conspecific CP, heterospecific HP, selfing SF.
# DonorHP : HP donor Genus_species.
# DonorHP.ID : HP donor Genus_species_ID; "NO" for "CP" and "SF" treatment types.
# DonorCP.ID : CP donor Genus_species_ID; same as the recipient ID for "SF" treatment type.
# Treatment.date : Treatment date (day/month/year).
# Pair.ID : Unique ID for each pair; each HP or SF is associated with a conspecific control in a pair.
# Recipient.IUCN : IUCN status of Recipient in CH.
# Recipient.WA.IUCN : IUCN status of Recipient in Westliche Zentralalpen, roughly overlapping with Wallis.
# Recipient.endangered: Dichotomous variable for Recipient; 0 when IUCN status LC, 1 in all other cases.
# Donor.IUCN : IUCN status of Donor in CH.
# Donor.WA.IUCN : IUCN status of Donor in Westliche Zentralalpen, roughly overlapping with Wallis.
# Donor.endangered : Dichotomous variable for Donor; 0 when IUCN status LC, 1 in all other cases.
# PD : Phylogenetic distance Recipient-Donor (from Daphne tree).
# Seed.counts : Seed number; integer.
Sharing/Access information
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Code/Software
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Methods
Species used
We used a total of eight species with different distribution and IUCN red list status within Switzerland. All species are co-occurring in the lime-rich crop fields habitat (“Caucalidion” according to the classification by Delarze, Gonseth, Eggenberg, & Vust, 2015), insect-pollinated and have overlapping flowering times in nature (Landolt et al., 2010; Lauber, Wagner, & Gygax, 2018). We classified species as “common” if their IUCN status in Switzerland was “least concern”, and as rare otherwise. IUCN status in Switzerland correlated strongly with number of observation within Switzerland pooled between the years 2000 and 2020 (cor: 0.86, p-value < 2.2*10-16). Breeding system (self-compatible vs self-incompatible) was extracted from the BioFlor database (Kuehn, Durka, & Klotz, 2004). To test the relationship between recipient-donor relatedness and heterospecific pollen interference, we constructed a phylogenetic tree for our species by pruning a modified version (Malecore, Dawson, Kempel, Müller, & van Kleunen, 2018) of the dated DaPhnE supertree of Central European plant species (Durka & Michalski, 2012) and then calculated the phylogenetic distance using the cophenetic function of the “ape” package (Paradis, E. Claude & Strimmer, 2004) in R.
Experimental set-up
We sowed all species into 12 cm x 17 cm trays filled with Seedling substrate (Klasmann-Deilmann GmbH, 49741 Geeste, Germany) and put them into the dark coolroom at -4°C for stratification between 5 and 8 weeks. Once seeds would start to germinate, we moved the trays to a greenhouse compartment. We transplanted seedlings into 11 cm x 11 cm x 12 cm pots filled with Selmaterra (fertilized heavy soil with 30% volume peat, see Table S 2). We randomized pots on tables of a single greenhouse compartment and watered as well as fertilized regularly. We treated aphids and fungi whenever necessary.
All species flowered between May 2021 and October 2021. To assure continuing of flowering, we regularly cut untreated flowers. To assess the effect size of heterospecific pollen interference, we performed hand pollinations among all species and measured seed set (yes/no) and seed number (counts). For the heterospecific pollen treatment, we prepared a saturated mix of conspecific pollen and heterospecific pollen and applied it to the stigma of the recipient flower. For each flower treated with heterospecific pollen mixture, we treated a second flower on the same plant individual on the same day with conspecific pollen only as a control, using the same conspecific pollen donor that we used for the heterospecific pollen mix. The two flowers with heterospecific and conspecific treatment would constitute a pair with the same “pair ID”. Pollen grain number per anther differed greatly depending on individual and on anther ripeness, thus we standardized treatment by always applying a pollen amount above saturation level. We extracted the pollen for the treatments from the anthers by tapping them on a glass slide and with the help of tweezers, and then mixed it for the heterospecific treatment using tweezers. We then applied the pollen mixture (HP) or the conspecific pollen (CP) to the open stigma of the recipient flower. To avoid selfing, we emasculated recipient flowers by removing the anthers some days before treatment. For some species (Bupleurum rotundifolium, Fallopia convolvulus, Myosotis arvensis), anther removal would cause too much flower damage due to the small size, thus anthers were not removed. For these species, selfing could not be completely excluded.
For each donor-recipient combination, we treated between 2 and 16 flower pairs (HP and CP; median: 12 flower pairs per donor-recipient combination). We collected seeds after ripening, and counted them either by hand or by using an imaging method with imageJ (Abramoff, Magalhaes, & Ram, 2004).