Fungi

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Fungi and animals are more closely related to each other than they are to plants or other eukaryotes.

DNA evidence suggests that fungi are most closely related to unicellular nucleariids while animals are most closely related to unicellular choanoflagellates.

This suggests that fungi and animals evolved from a common flagellated unicellular ancestor and multicellularity arose separately in the two groups.

The oldest undisputed fossils of fungi are only about 460 million years old.

Slide 17

Fungi and their close relatives

Animals (and their close

protistan relatives)

Other fungi

Nucleariids

Chytrids

UNICELLULAR,

FLAGELLATED

ANCESTOR

Fungi

Opisthokonts

Slide 18

The Move to Land

Fungi were among the earliest colonizers of land and probably formed mutualistic ++ relationships with early land plants.

Chytrids (phylum Chytridiomycota) are found in freshwater and terrestrial habitats.

They can be decomposers, parasites, or mutualists.

Chytrids are unique among fungi in having flagellated spores, called zoospores.

Slide 19

Fungus Diversity

Chytrids (1,000 species)

Zygomycetes (1,000 species)

Hyphae

25 µm

Glomeromycetes (160 species)

Fungal hypha

Ascomycetes (65,000 species)

Basidiomycetes (30,000 species)

Slide 20

Zygomycetes

The zygomycetes (phylum Zygomycota) exhibit great diversity of life histories.

They include fast-growing molds, parasites, and commensal symbionts.

The zygomycetes are named for their sexually produced zygosporangia.

Zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions.

Slide 21

Life Cycle of the zygomycete Rhizopus black bread mold

Rhizopus

growing

on bread

SEXUAL

REPRODUCTION

Young

zygosporangium

(heterokaryotic)

Gametangia with

haploid nuclei

Mating

type (–)

Mating

type (+)

Diploid (2n)

Haploid (n)

Heterokaryotic (n + n)

PLASMOGAMY

Key

Diploid

nuclei

Zygosporangium

100 µm

KARYOGAMY

MEIOSIS

Sporangium

Spores

Dispersal and

germination

ASEXUAL

REPRODUCTION

Dispersal and

germination

Sporangia

Mycelium

50 µm

Slide 22

Some zygomycetes, such as Pilobolus, can actually “aim” their sporangia toward conditions associated with good food sources.

0.5 mm