Phylogenetics and Classification: A Case Study with Chrysids

Disclaimer: this is not an information post, but a homework one. The task was to use the phylogenetic trees below to make an identification key, preferably dichotomous. To get the full marks, the key also has to be easy to use, i.e. with clearer characters (admittedly biased towards the entomologists with practical experience).

As background, these are cladograms for families of the Chrysidoidea (formerly known as Bethyloidea). The chrysids are the third, lesser known superfamily of stinging wasp (Aculeata); the other two superfamilies are the Vespidae (ants, wasps) and Apidae (bees). The Aculeata are defined by the modification of their ovipositor into a stinger and the somewhat related loss of female cerci.

Aculeata Phylogeny (from Grimaldi & Engel's Evolution of the Insects)

The chrysids are commonly called jewel, gold or cuckoo wasps. The seven families comprising them are: Plumaridae, Scolebythidae, Bethylidae, Chrysididae, Sclerogibbidae, Embolemidae and Dryinidae. All but most dryinids are ectoparasites, but the defining feature of the chrysids is not parasitism, but sexual unimorphism of the antennae (bees and wasps have sexually dimorphic antennae with males having more antennomeres than females). Another easily-recognisable character is the female’s enlarged femora and the exposed seventh metasomal tergum of the female (they sound like cryptic characters on paper, but one look under a stereomicroscope is enough to tell the difference between a bee and a chrysid).

The point of this exercise is not only to introduce cladograms, but also for students to get a feel for what kind of characters can go into a phylogenetic analysis, and for them to see for themselves that while phylogenetics may give us some ‘unintuitive’ results (“termites are cockroaches?!”), it is much more accurate than using vague terms, or even morphometric data, as is almost standard practice in field guides. The chrysids were chosen because the source paper (see below) is wonderful in its presentation. The exercise is also good for thinking; puzzle lovers will enjoy it. The moral of the exercise is: phylogenetics is the only correct way to classify organisms.

All cladograms and data come from: Carpenter. 2007. What do we know about chrysidoid (Hymenoptera) relationships? Zoologica Scripta 28, 215-231.

Labeling convention (c/ped from source): “Character numbers are above the hashmarks; state changes are shown below, with the respective primitive and derived conditions separated by a `>’. Filled hashmarks indicate a unique derivation, grayscale are convergent derivations, while open are reversals (unique or convergent).”

The answers here are mine. More creative (and still correct) ones were given in. I applaud them.

The formatting is a bit screwed here. Sorry.

Chrysidoidea families:
1a.    M + Cu present……………………..Plumariidae
1b.    M + Cu absent………………………Go to 2

2a.    Metapostnotum not constricted………..Scolebythidae
2b.    Metapostnotum constricted……………Go to 3

3a.     Furcula present…………………….Go to 4
3b.    Furcula absent……………………..Go to 5

4a.     Palpal formula 5:3………………….Chrysididae
4b.    Palpal formula 6:3………………….Bethylidae

5a.    Palpal formula 5:3………………….Sclerogibbidae
5b.    Palpal formula 6:3………………….Go to 6

6a.     Forewing with five cells…………….Dryinidae
6b.    Forewing with six cells……………..Embolemidae

Plumariidae genera:
1a.    Narrow clypeus……………………..Go to 2
1b.    Transverse clypeus………………….Go to 3

2a.     3 labial palpi……………………..Plumarius
2b.    2 labial palpi……………………..Myrmecopterina

3a.     Pronotal collar present……………..Myrmecopterinella
3b.    Pronotal collar absent………………Go to 4

4a.    1 labial palp………………………Maplurius
4b.    2 labial palpi……………………..Plumaroides

Scolebythid genera:
1a.     1 hindtibial spur…………………..Go to 2
1b.    2 hindtibial spurs………………….Go to 4

2a.    Pronotal collar present……………..Libanobythus
2b.    Pronotal collar absent………………Go to 3

3a.    Metapostnotum not apparent…………..Dominibythus
3b.    Distinct metapostnotum………………Ycaploca

4a.    Occipital carina present…………….Clystopsenella
4b.    Occipital carina absent……………..Scolebythus

Dryinidae subfamilies:
1a.    Female foreleg first claw regular-sized.Aphelopinae
1b.    Female foreleg first claw enlarged……Go to 2

2a.    Female rhinaria present……………..Go to 3
2b.    Female rhinaria absent………………Go to 7

3a.    Female mandible unidentate…………..Transdryininae
3b.    Female mandible quadridentate………..Go to 4

4a.    Pronotal tubercles present…………..Dryininae
4b.    Pronotal tubercles absent……………Go to 5

5a.    Female subocular sulcus absent……….Gonatopodinae
5b.    Female subocular sulcus present………Go to 6

6a.     One enlarged claw tooth……………..Apodryininae
6b.    No enlarged claw teeth………………Plesiodryininae

7a.    Epicnemium absent…………………..Bocchinae
7b.    Epicnenium visible………………….Go to 8

8a.    One enlarged claw tooth……………..Conganteoninae
8b.    No enlarged claw teeth………………Go to 9

9a.    Two midtibial spurs…………………Laberitinae
9b.    One midtibial spur………………….Anteoninae

Bethylidae subfamilies/tribes
1a.     Bifid claws………………………..Bethylinae
1b.     Toothed or simple claws……………..Go to 2

2a.    Female ocelli absent………………..Pristocerinae
2b.    Female ocelli present……………….Go to 3

3a.    Heavy sculpturing…………………..Mesitiinae
3b.    Light sculpturing…………………..Epyrinae

Chrysididae subfamilies/tribes:
1a.    Scapal basin absent…………………Cleptinae
1b.    Scapal basin present………………..Go to 2

2a.    Pronotal lobe adjacent to tergula…….Go to 3
2b.    Pronotal lobe separate………………Go to 4

3a.    Prothorax freely moveable……………Amiseginae
3b.    Prothorax fused to metathorax………..Loboscelidiinae

4a.    Claws edentate……………………..Go to 5
4b.    Claws unidentate……………………Go to 6

5a.    Sternum II spots present…………….Chrysidini
5b.    Sternum II spots absent……………..Parnpini

6a.    2 terga……………………………Allocoeliini
6b.    3 terga……………………………Elampini

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