Pollen essential amino acids shape bat-flower interaction networks

Although pollen consumption by phytophagous bats has long been documented,
the role of its protein and amino acid content in driving plant–pollinator
interactions remains largely overlooked. Since animals can synthesise
non-essential amino acids (NEAA) but rely on dietary for essential amino
acids (EAA), pollen may serve as a reward through an amino acid
composition that is tailored to the nutritional demands of pollinators.
This study examines how pollen protein and amino acid composition
influence year-round and seasonal bat-flower interaction networks in the
Pantanal floodplain through extensive, long-term, bat-centred sampling. We
predicted that EAA-richer plant species would play central roles within
the networks by exhibiting a higher normalised degree (i.e., how many bat
species a given plant species interact with) and greater interaction
strength (i.e., how intense the interactions are) in the network. The
year-round network consisted of eight plant species with chiropterophilous
traits and 12 bat species from five feeding guilds. Protein content in the
pollen of chiropterophilous plants ranged from 12% to 34%, with all
essential and most non-essential amino acids present. Bats from all guilds
interacted more frequently with plants whose pollen was richer in EAA, but
notably more so with insectivorous and carnivorous bats during the dry
season. In contrast, nectarivorous, frugivorous, and omnivorous bats
maintained interactions year-round with a full range of plant species. The
year-round bat–flower interaction network showed low specialisation H2’ =
0.29) and modularity (M = 0.28), forming four distinct modules. In this
network, the two plants with the highest richness of EAA formed separate
modules and interacted with more bat species. Moreover, the richness of
EAA in pollen strongly and positively affected the plant species’
normalised degree and interaction strength. The great richness of EAA and
pollen protein biomass, along with the effect of pollen EAA richness on
bat-flower interactions, may suggest that the pollen of chiropterophilous
flowers has evolved in response to the dietary requirements of
phytophagous bats. Our findings underscore the essential role of pollen,
not just nectar, as a key reward for attracting flower-visiting bats, and
therefore highlights pollen content as an important driver structuring
pollination networks.