Dispersal and trait evolution: Did New Zealand’s sequestrate fungi evolve unique traits to match bird sensory ecologies?

Abstract

Many plants use animal vectors for dispersal. Fruit and seed propagules attract animals using visual and olfactory signals. Signal evolution is driven by the receiver’s sensory ecology, and ability to detect colours and smells. Some fungi also evolve signals to attract animals for spore dispersal. These signals should match the potential disperser’s sensory systems. Globally, truffle-like fungi (TLF) are generally dull-coloured, strong-scented and subterranean, matching mammalian foraging behaviour and sensory preferences. New Zealand's (NZ) faunal ecology is uniquely dominated by birds and reptiles. Here, TLF are brightly coloured, forest floor emergent sporocarps, which resemble the fruits of native flora, matching bird and reptile preferences for contrasting colours. I hypothesise that NZ’s TLF and fruiting plants evolved convergent visual cues in response to the sensory ecology and selection pressures imposed by endemic bird dispersers. In chapter 1, I provide a brief introduction, then chapter 2 offers a deeper, systematic literature review compiling all records of interactions between native birds and fruits, and their traits. These preliminary fruit colour and size traits are then compared to TLF. I found that NZ birds interact with fruits of all colours. Colour interactions were best explained by diet, not phylogeny, with dietary generalists interacting with diverse fruits resembling TLF. Bird gape sizes did determine fruit sizes and may also constrain TLF sizes. TLF and fruit of the same colour were the same size, indicating highly specific, convergent evolution, potentially a result of specific bird interactors. In chapter 3, I collect and analyse the spectral reflectances of 10 species of NZ’s TLF and 32 species of fruits from sympatric plants. I found that TLF and fruit spectrograms are indistinguishable, however, brightness is varied. In chapter 4, I avoid human colour vision biases and model fruit and TLF spectral reflectances using bird vision systems, testing colour similarities and discernment. I found that bird models could not discern between many fruits and TLF. Generalist frugivores were least perceptive, suggesting they are the true dispersal targets of TLF. Birds that contribute to fruit dispersal likely disperse TLF, driving the evolution of convergent colour and size characteristics in these endemic organisms. This is the first comprehensive investigation of trait convergence of NZ endemic fruit and TLF, providing an interesting perspective of the dispersal syndrome hypothesis in the context of NZ’s endemic fungi.