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Capniidae

(Family)

Overview

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Capniidae, the small winter stoneflies, is a family of insects in the stonefly order (Plecoptera). It constitutes one of the largest stonefly families, containing some 300 species distributed throughout the Holarctic. Their closest relatives are the (Leuctridae).1]

Many species are endemic to small ranges, perhaps due to the family's tendency to evolve tolerance for cold (isolating populations in mountain valleys) and winglessness (inhibiting dispersal)[2]. Indeed, some wingless Capniidae ? e.g. the Lake Tahoe Benthic Stonefly ("Capnia" lacustra[3]) or Baikaloperla spp. ? spend their entire life cycle underwater and do not disperse from their native lakes at all[4].

Description and ecology

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Adult Capniidae, as their common name implies, typically small Plecoptera; while most are less than 1 cm long with some measuring just 4 mm as adults, a few are as large as 25 mm (1 inch) at adulthood. The adults emerge from the water in winter and are often found walking around on the snow. Characteristic are the wings with at most one cubital crossvein, and the paraprocts (anal lobes) whose inner lobes form a tube closed on the underside by the outer lobes.[2]

Nymphs of small winter stoneflies typically have a very elongated and slender body, similar to those of rolled-winged stoneflies (Leuctridae). However, the groove along the abdomen, from segment 1 to 9, is generally very pronounced.[2]

The nymphs dwell in the hyporheic zone, the interface between stream water and groundwater. Only immediately before moulting into the adult form will the nymphs move out of the substrate and appear on the stream bed. Thus, although they may be plentiful in clean rivers and streams, they are seldom encountered in standard samples of benthos.[2]

Systematics and taxonomy

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The family Capniidae is often considered to be monotypic as to subfamily, with the Capniinae being inserted at that rank. However, this is rather pointless; in any case the phylogeny, systematics and taxonomy of the small winter stoneflies are highly confused. There appear to be two very basal genera and presumably two larger clades which conceivably could be considered subfamilies. But the phylogeny of the Capni idae is by no means robustly resolved, with about one-third of the named genera of uncertain position. Hence, any subdivision beyond the generic level is premature.[2]

Furthermore, the type genus Capnia is probably not monophyletic and in serious need of splitting up. The type species Capnia nigra and its closest relatives would retain their genus name; they are closely related to Capnura. The North American species at least for the largest part are closer to Mesocapnia; other "Capnia" are closest to Bolshecapnia as it seems. Finally, there is a fourth group of rather uncertain position in the main assemblage of Capniidae.[2]

A rough layout of the suspected phylogeny can be given as follows:

Basal genera

Suspected clade/subfamily 1

Suspected clade 2/subfamily Capniinae sensu stricto

Incertae sedis as to clade 1 or 2

Footnotes

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  1. ^ Nelson (1996a,b)
  2. ^ a b c d e f Nelson (1996b)
  3. ^ Capnia is not monophyletic and this species is suspected to belong elsewhere (see "Systematics and taxonomy" section)
  4. ^ Holst (2000)
b>Capniidae, the small winter stoneflies, is a family of insects in the stonefly order (Plecoptera). It constitutes one of the largest stonefly families, containing some 300 species distributed throughout the Holarctic. Their closest relatives are the (Leuctridae).1]

Many species are endemic to small ranges, perhaps due to the family's tendency to evolve tolerance for cold (isolating populations in mountain valleys) and winglessness (inhibiting dispersal)[2]. Indeed, some wingless Capniidae ? e.g. the Lake Tahoe Benthic Stonefly ("Capnia" lacustra[3]) or Baikaloperla spp. ? spend their entire life cycle underwater and do not disperse from their native lakes at all[4].

Description and ecology

[ Back to top ]

Adult Capniidae, as their common name implies, typically small Plecoptera; while most are less than 1 cm long with some measuring just 4 mm as adults, a few are as large as 25 mm (1 inch) at adulthood. The adults emerge from the water in winter and are often found walking around on the snow. Characterist ic are the wings with at most one cubital crossvein, and the paraprocts (anal lobes) whose inner lobes form a tube closed on the underside by the outer lobes.[2]

Nymphs of small winter stoneflies typically have a very elongated and slender body, similar to those of rolled-winged stoneflies (Leuctridae). However, the groove along the abdomen, from segment 1 to 9, is generally very pronounced.[2]

The nymphs dwell in the hyporheic zone, the interface between stream water and groundwater. Only immediately before moulting into the adult form will the nymphs move out of the substrate and appear on the stream bed. Thus, although they may be plentiful in clean rivers and streams, they are seldom encountered in standard samples of benthos.[2]

Systematics and taxonomy

[ Back to top ]

The family Capniidae is often considered to be monotypic as to subfamily, with the Capniinae being inserted at that rank. However, this is rather pointless; in any case the phylogeny, systematics and taxonomy of the small winter stoneflies are highly confused. There appear to be two very basal genera and presumably two larger clades which conceivably could be considered subfamilies. But the phylogeny of the Capniidae is by no means robustly resolved, with about one-third of the named genera of uncertain position. Hence, any subdivision beyond the generic level is premature.[2]

Furthermore, the type genus Capnia is probably not monophyletic and in serious need of splitting up. The type species Capnia nigra and its closest relatives would r etain their genus name; they are closely related to Capnura. The North American species at least for the largest part are closer to Mesocapnia; other "Capnia" are closest to Bolshecapnia as it seems. Finally, there is a fourth group of rather uncertain position in the main assemblage of Capniidae.[2]

A rough layout of the suspected phylogeny can be given as follows:

Basal genera

Suspected clade/subfamily 1

Suspected clade 2/subfamily Capniinae sensu stricto

Incertae sedis as to clade 1 or 2

Footnotes

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  1. ^ Nelson (1996a,b)
  2. ^ a b c d e f Nelson (1996b)
  3. ^ Capnia is not monophyletic and this species is suspected to belong elsewhere (see "Systematics and taxonomy" section)
  4. ^ Holst (2000)

References

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Taxonomy

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The Family Capniidae is a member of the Superfamily Nemouroidea. Here is the complete "parentage" of Capniidae:

The Family Capniidae is further organized into finer groupings including:

Genera

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Allocapnia

[more]

Apteroperla

[more]

Baikaloperla

[more]

Bolshecapnia

[more]

Capnella

[more]

Capnia

[more]

Capniella

[more]

Capnioneura

[more]

Capnopsis

[more]

Capnura

[more]

Eocapnia

Eucapnopsis

[more]

Isocapnia

[more]

Mesocapnia

[more]

Nemocapnia

[more]

Paracapnia

[more]

Takagripopteryx

Utacapnia

[more]

At least 11 species and subspecies belong to the Genus Utacapnia.

More info about the Genus Utacapnia may be found here.

References

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Sources

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Last Revised: August 24, 2012
2012/08/24 13:26:46