1.1: Time-series data can distinguish between species destined for
invasion and those that adapt in situ
One of the oldest postulations in the field of invasion biology is that
some species are “predisposed” to invasiveness (Baker, 1965). In other
words, some traits that facilitate spread in a new environment are not
adaptations that arise following colonization (see Part 4), but instead
exist in native populations prior to transport (Figure 2). For example,
the kudzu bug (Megacopta cribraria ) was introduced from Asia to
North America where it initially grew on kudzu, but within 9 months of
detection had begun exploiting soy crops. Studies in the native range
had shown that the genotype of the symbiont CandidatusIshikawaella capsulata (‘Ishikawaella’ hereafter) mediatesM. cribraria ’s ability to grow on soy (Hosokawa, Kikuchi, Nikoh,
Shimada, & Fukatsu, 2006). Therefore, it was initially unclear whether
the switch to soy was enabled by the evolution of Ishikawaella in the
invasive range. Brown et al. (2014) inferred the evolution of the
symbiont Ishikawaella by sequencing its genome at various locations,
including the founding population in the year it was first detected, and
at different time points since. Their analysis revealed that the
founding population closely resembled native Japanese Ishikawaella
samples known to enable growth on soy, with little evidence of allele
frequency changes during invasion. This suggests that M.
cribraria and its symbiont Ishikawaella had arrived in the US already
able to spread on soy plantations. Though the 750kbp Ishikawaella genome
is sequenced at scale with relative ease, this study exemplifies the
significant and under-exploited benefits of WGR time-series data as a
means of tracking genome-wide shifts in allele frequency during
biological invasion. This approach could in principle be applied to any
invasive species to distinguish between pre- and post-introduction
adaptation.