15
Since spectral signals are integrated measures of phenotype, spectra should be more
dissimilar among distantly related groups than among close relatives (CavenderBares et al. 2016b; McManus et al. 2016; Schweiger et al. 2018). This expectation
can be seen from models of evolution in which traits change over time following a
random walk (Brownian motion process; Fig. 2.1b) (O’Meara et al. 2006; Meireles
et al., Chap. 7). In cases of convergent evolution—where natural selection causes
distant relatives to evolve similar functions in similar environments—however, phenotypes can be more similar than expected under Brownian motion.
This hierarchy of life is relevant to RS of plant diversity because certain depths
of the tree of life may be more accurately detected than others at different spatial
resolutions and geographic regions. For example, it could be easier to detect deeper
levels in the hierarchy (such as genera or families) in hyper-diverse communities
than in shallow levels (such as species) because deep splits tend to have greater trait
divergence. Meireles et al. (Chap. 7) further explain why and how phylogenetic
information can be leveraged to detect plant diversity.
2.3 The Making of a Phenotype: Phylogeny, Genes,
and the Environment
The phenotype of an organism is the totality of its attributes, and it is quantified in
terms of its myriad functions and traits. The phenotype of an organism is a product
of the interaction between the information encoded in its genes—the genotype—
and the environment over the course of development. Understanding the relative
influence of gene combinations, environmental conditions, and ontogenetic stage is
an active area of investigation across different disciplines (Diggle 1994; Sultan
2000; Des Marais et al. 2013; Palacio-López et al. 2015).
Although genotypes often play a critical role in determining phenotypic outcomes, many processes can result in mismatches between genotype and phenotype.
One of the most well documented of these processes is known as phenotypic plasticity—when organisms with the same genotype display different phenotypes, usually
in response to different environmental conditions (Bradshaw 1965; Scheiner 1993;
Des Marais et al. 2013). Plasticity can also result in distinct genotypes developing
similar phenotypes when growing under the same environmental conditions.
A similar story can be told about the relationship of phenotypic similarity and
phylogenetic relatedness. As we have seen earlier, closely related taxa are expected
to be more similar to each other than distantly related taxa. However, convergent
evolution can lead to plants from different branches of the tree of life to evolve very
similar traits—such as succulents, which are found within both euphorbia and very
distantly related cacti taxa.
The fact that phenotypes can be, but not necessarily are, directly related to
specific genotypes and phylogenetic history should be considered when remotely
sensing biodiversity. Only phenotypes can be remotely sensed directly. Genetic and
phylogenetic information can only be inferred from spectra to the degree that
2 Applying Remote Sensing to Biodiversity Science
Since spectral signals are integrated measures of phenotype, spectra should be more
dissimilar among distantly related groups than among close relatives (CavenderBares et al. 2016b; McManus et al. 2016; Schweiger et al. 2018). This expectation
can be seen from models of evolution in which traits change over time following a
random walk (Brownian motion process; Fig. 2.1b) (O’Meara et al. 2006; Meireles
et al., Chap. 7). In cases of convergent evolution—where natural selection causes
distant relatives to evolve similar functions in similar environments—however, phenotypes can be more similar than expected under Brownian motion.
This hierarchy of life is relevant to RS of plant diversity because certain depths
of the tree of life may be more accurately detected than others at different spatial
resolutions and geographic regions. For example, it could be easier to detect deeper
levels in the hierarchy (such as genera or families) in hyper-diverse communities
than in shallow levels (such as species) because deep splits tend to have greater trait
divergence. Meireles et al. (Chap. 7) further explain why and how phylogenetic
information can be leveraged to detect plant diversity.
2.3 The Making of a Phenotype: Phylogeny, Genes,
and the Environment
The phenotype of an organism is the totality of its attributes, and it is quantified in
terms of its myriad functions and traits. The phenotype of an organism is a product
of the interaction between the information encoded in its genes—the genotype—
and the environment over the course of development. Understanding the relative
influence of gene combinations, environmental conditions, and ontogenetic stage is
an active area of investigation across different disciplines (Diggle 1994; Sultan
2000; Des Marais et al. 2013; Palacio-López et al. 2015).
Although genotypes often play a critical role in determining phenotypic outcomes, many processes can result in mismatches between genotype and phenotype.
One of the most well documented of these processes is known as phenotypic plasticity—when organisms with the same genotype display different phenotypes, usually
in response to different environmental conditions (Bradshaw 1965; Scheiner 1993;
Des Marais et al. 2013). Plasticity can also result in distinct genotypes developing
similar phenotypes when growing under the same environmental conditions.
A similar story can be told about the relationship of phenotypic similarity and
phylogenetic relatedness. As we have seen earlier, closely related taxa are expected
to be more similar to each other than distantly related taxa. However, convergent
evolution can lead to plants from different branches of the tree of life to evolve very
similar traits—such as succulents, which are found within both euphorbia and very
distantly related cacti taxa.
The fact that phenotypes can be, but not necessarily are, directly related to
specific genotypes and phylogenetic history should be considered when remotely
sensing biodiversity. Only phenotypes can be remotely sensed directly. Genetic and
phylogenetic information can only be inferred from spectra to the degree that
2 Applying Remote Sensing to Biodiversity Science