Nepenthes pitchers versus thermogenic flowers: Thermal patterns and their role in prey capture and pollination

Abstract

Prey capture in Nepenthes and pollination in angiosperms are two antithetical events; one designed to trap insects and other arthropods (carnivory) and the other to transfer pollen through pollinators (reproduction). In this study infrared thermography is extensively used to obtain thermal profiles of Nepenthes pitchers and thermogenic flowers in field conditions. N. khasiana pitchers displayed below ambient temperatures during evening-night-morning hours (5 pm to 8-9-10 am); pitcher spots recorded lowest and highest temperatures as 14.4 (6-7 am) and 45.6{degrees}C (2 pm), respectively. In the evening-night-morning hours top pitcher spots displayed significant decrease (upto 6.7{degrees}C) from the ambient temperature. The average humidities in the night and day periods were 77.15% and 50.15%, respectively. Thermographic tracking of the pitcher (lid) opening in N. khasiana demonstrated initial wet pitcher in night, which gradually switched to a relatively dry surface in the morning-day times; but the peristome region retained the wetness till 10.30 a.m. The prey capturing zones in Nepenthes pitchers (peristome, lid and their intersection) are colder favoring prey capture, whereas in thermogenic flowers, floral portions are hotter, providing the thermal requirements for the pollinator. In thermogenic plants, floral zones assist pollination by offering a thermal reward through enzymatic processes; but Nepenthes traps achieve lower temperature spots by physical (surface microstructures), chemical (extrafloral nectar) and ecological (rain, humidity) factors.