Pollen dispersal patterns differ among sites for a wind-pollinated species and an insect-pollinated species

MATERIALS AND METHODS We assessed pollen dispersal patterns of A. tuberculatus at one roof and one ground site in 2014 and of both A. tuberculatus and S. lycopersicum at two roof and two ground sites in 2015. Because methods and results were similar between the two years, and the 2015 study was more comprehensive, only methods and results for 2015 are presented here. A summary of the results from 2014 can be found in Appendix S1 (see the Supplementary Data with this article) and the results from the 2014 analysis can be found in Appendix S2. Study species – Amaranthus tuberculatus was chosen as the wind-pollinated species because amaranths grow well in urban areas (Del Tredici, 2010; Aloisio et al., 2016), it is dioecious (Hager et al., 1997), and there have been no individuals reported in the counties where our study sites were located (Moore et al., 2012; USDA NRCS, 2017). Seeds from both an Iowa, USA population (Hinz and Owen, 1997) and a Mississippi, USA population (Nandula et al., 2013) of A. tuberculatus were used in the 2014 experiment. In the 2015 experiment, only plants from the Iowa population were used due to low germination in the Mississippi population seeds. We chose S. lycopersicum as the insect-pollinated species because members of the Solanaceae grow well in urban environments (Del Tredici, 2010). S. lycopersicum is most commonly buzz-pollinated (Buckmann and Hurley, 1978) by bee species (e.g. bumble bees, sweat bees; Teppner, 2005), although bees that do not buzz pollinate (e.g. honey bees), have been shown to chew through the anther cone to obtain pollen (Deprá et al., 2014). Furthermore, although S. lycopersicum typically self-fertilizes, the NC4 S. lycopersicum breeding line (Panthee and Gardner, 2013) produces male-sterile and male-fertile offspring. Also, the ms-10 male-sterility gene is tightly-linked to the aa gene for stem color, with 90% of male-sterile plants having green stems and 90% of male-fertile plants having purple stems. As a result, we were able to separate most male-sterile and male-fertile plants prior to the onset of flowering and pollen production. Greenhouse methods – Seeds were germinated and seedlings were grown in a greenhouse at the Louis Calder Center (Fordham University) field station in Armonk, New York, USA during the spring of 2015 ((S. lycopersicum – April/May; A. tuberculatus – May/June), following Butcher et al. (2020). Briefly, seeds were germinated in 53 x 28 x 5 cm (l x w x d) potting trays (Griffin Greenhouse Supplies, Tewksbury, Massachusetts, USA) containing Sungro Sunshine Soil-mix 4 (Sungro Horticulture, Agawam, Massachusetts, USA) supplemented with Osmocote 14-14-14 fertilizer (Scotts Miracle-Gro, Marysville, Ohio, USA). Trays were bottom-watered every other day with well water until the soil was saturated. Seedlings were transplanted to 10-cm dia (0.57 L) pots (Griffin Greenhouse Supplies, Tewksbury, Massachusetts, USA) when all seedlings had reached 5 to 10 cm tall (measured from soil to apical meristem). Seedlings were grown in Sungro Sunshine Soil-mix 4, and watered to throughflow with well water every other day. Before onset of flowering, S. lycopersicum were separated into pollen receptors and donors based on stem color. Prior to placing the plants at study sites, pollen receptors and donors of both species were confirmed by flower morphology, inflorescences were removed to exclude seeds or fruits produced as a result of pollination in the greenhouse, and plants were transplanted to 11.4 L pots (Griffin Greenhouse Supplies, Tewksbury, Massachusetts, USA) with Sungro Sunshine Soil-mix 4 (Sungro Horticulture, Agawam, Massachusetts, USA). These plants served as the parent plants in the study. We collected leaf tissue (1-2 young leaves) from each plant for genotyping. Study sites – Parent plants were placed in experimental arrays at four sites in the New York metropolitan area, which is located in the northeast USA: 1) Fordham University’s Rose Hill Campus (Rose Hill) in Bronx, New York, USA, 2) the Javits Convention Center (Javits) in New York, New York, USA, 3) Fordham University’s Louis Calder Center (Calder) in Armonk, New York, USA and 4) the Queens Zoo (Queens Zoo) in Corona, New York, USA (Fig. 1). At each site, 12 pollen donor plants of each species (i.e. male A. tuberculatus plants and male-fertile S. lycopersicum plants) were placed in the main sector of each site (pollen donor group; Fig. 2). A. tuberculatus and S. lycopersicum pollen receptor plants were also placed in the main sector, in groups of two, by species, starting at 1 m and at then at increasing distances from the pollen donor group (Table 1; Fig. 2). Additionally, A. tuberculatus and S. lycopersicum pollen receptor plants were placed in groups of two, by species, in up to three nearby non-contiguous sectors. The number of pollen receptor plants, the maximum distance between the pollen donor group and pollen receptor plants, and the number of non-contiguous sectors...