Phylogenetic analyses suggest that fungi evolved from a flag- ellated ancestor. While the majority of fungi lack flagella, some of the earliest-diverging lineages of fungi (the chytrids, as we’ll discuss shortly) do have flagella. Moreover, most of the protists that share a close common ancestor with animals and fungi also have flagella. DNA sequence data indicate that these three groups of eukaryotes—the fungi, the animals,
and their protistan relatives—form a clade (Figure 31.8). As discussed in Chapter 28, members of this clade are called opisthokonts, a name that refers to the posterior (opistho-) location of the flagellum in these organisms.
DNA sequence data also indicate that fungi are more closely related to several groups of single-celled protists than they are to animals, suggesting that the ancestor of fungi was unicel- lular. One such group of unicellular protists, the nucleariids, consists of amoebas that feed on algae and bacteria. DNA evi- dence further indicates that animals are more closely related
to a different group of protists (the choanoflagellates) than
they are to either fungi or nucleariids. Together, these results suggest that multicellularity must have evolved in animals and fungi independently, from different single-celled ancestors.
Using molecular clock analyses, scientists have estimated that the ancestors of animals and fungi diverged into sepa- rate lineages 1–1.5 billion years ago. Fossils of certain unicel- lular, marine eukaryotes that
lived as early as 1.5 billion
years ago have been inter-
preted as fungi, but those
claims remain controversial.
Furthermore, although most
scientists think that fungi
originated in aquatic envi-
ronments, the oldest fossils
that are widely accepted
as fungi are of terrestrial
species that lived about
460 million years ago
(Figure 31.9). Overall, more
50 μm
▲ Figure 31.9
hyphae and spores from the Ordovician period (about 460 million years ago) (LM).
Fossil fungal
Phylogenetic analyses suggest that fungi evolved from a flag- ellated ancestor. While the majority of fungi lack flagella, some of the earliest-diverging lineages of fungi (the chytrids, as we’ll discuss shortly) do have flagella. Moreover, most of the protists that share a close common ancestor with animals and fungi also have flagella. DNA sequence data indicate that these three groups of eukaryotes—the fungi, the animals,
and their protistan relatives—form a clade (Figure 31.8). As discussed in Chapter 28, members of this clade are called opisthokonts, a name that refers to the posterior (opistho-) location of the flagellum in these organisms.
DNA sequence data also indicate that fungi are more closely related to several groups of single-celled protists than they are to animals, suggesting that the ancestor of fungi was unicel- lular. One such group of unicellular protists, the nucleariids, consists of amoebas that feed on algae and bacteria. DNA evi- dence further indicates that animals are more closely related
to a different group of protists (the choanoflagellates) than
they are to either fungi or nucleariids. Together, these results suggest that multicellularity must have evolved in animals and fungi independently, from different single-celled ancestors.
Using molecular clock analyses, scientists have estimated that the ancestors of animals and fungi diverged into sepa- rate lineages 1–1.5 billion years ago. Fossils of certain unicel- lular, marine eukaryotes that
lived as early as 1.5 billion
years ago have been inter-
preted as fungi, but those
claims remain controversial.
Furthermore, although most
scientists think that fungi
originated in aquatic envi-
ronments, the oldest fossils
that are widely accepted
as fungi are of terrestrial
species that lived about
460 million years ago
(Figure 31.9). Overall, more
50 μm
▲ Figure 31.9
hyphae and spores from the Ordovician period (about 460 million years ago) (LM).
Fossil fungal
การแปล กรุณารอสักครู่..