Cheater or mutualist? Novel florivory interaction between nectar‐rich Crotalaria cunninghamii and small mammals

Abstract

Animals visit flowers to access resources and by moving pollen to conspecific individuals act as pollinators. While biotic pollinators can increase the seed set of plants, other flower visitors can reduce seed set directly by damaging vital reproductive organs and indirectly by affecting the way the plant interacts with subsequent flower visitors. It is, therefore, vital to understand the varied effects of all visitors and not only pollinators on plant fitness, including those visitors that are temporally or spatially rare. We document the first known case of flower visitation by small mammals to Crotalaria cunninghamii (Fabaceae), a plant species morphologically suited to bird pollination. During a rain-driven resource pulse in the Simpson Desert in 2011, the rodents Mus musculus (Muridae) and Pseudomys hermannsburgensis (Muridae) visited flowers to remove nectar by puncturing the calyx. We investigated the effects of this novel interaction on the reproductive output of C. cunninghamii. Compared with another recent resource pulse in 2007, plants flowering during mammal visitation had five times as many inflorescences per plant, 90% more flowers per inflorescence, and two to three times more nectar per flower, but this nectar was 30% less sugar rich. Concurrently, rodent plagues were up to three times larger during this rain-driven resource pulse than during a previous pulse in 2007. Up to 75% of flowers had evidence of small mammal florivory, but this was not necessarily destructive, as up to 90% of fruit had the remains of florivory. Through a series of exclusion experiments, we found that small mammal florivory did not directly reduce seed set. We conclude that rain-driven resource pulses led to a unique combination of events that facilitated the novel florivory interaction. Our findings emphasize the dynamic nature of biotic interactions and the importance of testing the role of all visitors to pollination services.

Clock-dated phylogeny for 48% of the 700 species of Crotalaria (Fabaceae–Papilionoideae) resolves sections worldwide and implies conserved flower and leaf traits throughout its pantropical range

“…1 and Additional file 1 : Figure S1, Additional file 2 : Figure S2 and Additional file 3 : Figure S3) turned out to be highly conserved, which may reflect that the main pollinators of crotalarias, species in the long-tongued bee family Megachilidae with over 4,000 species, are abundant in ecosystems from arid habitats to tropical forests [ 7 , 10 , 11 , 26 ]). All Crotalaria flowers, even the honeyeater-pollinated Australian C. cunninghamii [ 50 ], have the same pollination mechanism in which the narrow keel beak serves as a cylinder and the style acts together with the anthers as a piston. No study has compared the effect of a spirally twisted or straight keel beak on pollen release, and Pohlhill’s (1982) suggestion that a twisted keel beak might better proportion pollen release does not match the finding that flowers with and without such keels have the same short life span and are visited by some of the same bee species ( C. micans and C. stipularia flowers function for c. four days, [ 10 , 11 , 26 ]: C. retusa flowers for one day; own observations show that flowers last for 3-4 days in C. pallida , and for 4-5 days in C. cunninghamii , C. novae-hollandiae , and C. velutina ).…”

“…Fitting with the predominant bee pollination, Crotalaria flowers are yellow, sometimes with red or brownish markings. Few species have white, blue, or greenish flowers; an example of a green-flowered species is the Australian C. cunninghamii , which presumably is pollinated by honeyeaters (Meliphagidae) [ 50 ].

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