Tegeticula antithetica - Yucca Moth

8/3/2019 Tegeticula antithetica - Yucca Moth

1/8

Tegeticula antithetica Yucca Moth

Tegeticula antithetica belongs to the order Lepidoptera and suborder

Glossata. It is a member of the Prodoxidae family (superfamily: Incurvarioidea),

which is commonly called Yucca Moths because of their close association with

Yucca plants. The Tegeticula and Parategeticula genera are the only two genera ofthe family that are obligate pollinators as well as herbivores of Yucca plants. Yucca

moths are famous for being one of the best-studied examples of coevolution

between a plant and insect, as the plants rely on adult moths for their pollination

and the moth larvae depend on developing seeds to complete their development [3].

Figure 1: A Yucca moth on a Yucca flower

Geographic Range

Yucca moths can be found wherever their host plants are located. In the case

ofT. antithetica, its host plant is the Joshua tree (Yucca brevifolia), located in the

Mojave Desert of the North American southwest, specifically southern California,

southern Nevada, southwestern Utah, and western Arizona (Figure 2)[1]. Other

related yucca plants and moths (Tegeticula and Parategeticula) are generally located

in the American west and northern Mexico.


2/8

Figure 2: Geographic distribution ofY. brevifolia and its two Tegeticula pollinators.

Map includes southern California, southern Nevada, southwestern Utah, and western Arizona. Y.

brevifolia distribution is outlined in white line, with the dashed line indicating the split in the two

Yucca varieties, brevifolia and vespertina. Black circles representT. synthetica and black squares

representT. antithetica

Morphology

T. antithetica is most closely related to T. synthetica because the two species

are sister taxa and diverged from a single pollinator species ofYucca brevifolia [1].The two moths may have allopatrically speciated in response to the Bouse

embayment, an estuarine extension that inundated low-lying areas of the Mojave

Desert region ~6.5 million years ago [2]. This may have caused the considerable

differences in stature and branching architecture between the eastern and western

versions of the Joshua tree (Figure 3) and its pollinators T. antithetica and T.

synthetica, respectively.

T. antithetica has a wingspan of 13.5-15 mm in males and 13-16 mm in

females. T. antithetica can be distinguished by arrow-shaped mark in the discal cell

of its forewing (Figure 4). T. antithetica is significantly smaller than its close relative

T. synthetica (Figure 5). The integuments are dark brown and the ventral side of the

female head has 20-25 sensory setae (the male having none) and the antennae areabout a third the length of the forewing.

The genitalia of the males also allow for distinguishing between the two

closely related species. The valvae ofT. antithetica have much smaller ventral

protrusions and a different number and distribution of spines on those protrusions

(Figure 6).


3/8

Figure 3: (A) Yucca brevifolia with high branching, asymmetric crown, and long narrow pistil ( inset)

typical of Yuccas pollinated by T. synthetica. (B) Y. brevifolia with low branching, symmetric crown,

and short thick pistil (inset) typical of Yuccas pollinated by T. antithetica. Photos not to scale


4/8

Figure 4: (A) Male T. antithetica and (B) Male T. synthetica. (C, inset)shows an enlarged image of the

arrow-shaped mark in the discal (central) cell of the T. antithetica forewing. The arrows are pointing

to the notable differences in the moths valvae (claspers). The scale bars in both A and B are 2.5 mm.

The hind wing in A is actually darker, but appears brighter because of a reflecting glare in the photo.


5/8

Figure 5: Half-images of female T. synthetica (left) and T. antithetica (right). Note the arrow-shaped

make on the forewing ofT. antithetica.

Figure 6: Male genitalia of (A) T. antithetica and (B) T. synthetica. The right valvae are shown for

both. Arrows indicate the differences in ventral protrusions of the valvae and differences of spine

number and distribution. Scale bars represent 0.5 mm.

Life Cycle, Ecology & Behavior

The female Tegeticula moth oviposits Joshua tree flowers by cutting throughthe ovary wall and extending her ovipositor down the stylar canal to lay eggs atop

the ovules. Then, the female pollinates the flower to ensure the production/

availability of seeds for her larvae to feed on (Figure 7) [2]. The female does this by

using unique tentacular mouthparts to collect pollen by dragging them across the

anthers. The moth compacts the pollen using the tentacular mouthparts and stores

it underneath her head. Recurring pollen collection through the moths lifetime

results in multiple pollen genotypes. After oviposition of the eggs, the female walks

up to the stigma, scrapes some pollen off of her batch using her tentacles, and places

the pollen on the style (see Video Clip) [4].

The eggs ofTegeticula hatch within a few days and then the larvae begin

immediately feeding on the developing yucca seeds, eating only a small proportion[5]. After feeding, the larva creates an exit path so it can escape the flower to find a

location to burrow itself. The larva waits inside the fruit for optimal weather

conditionsuntil rainy and usually at nightthen burrows into the ground where it

create a silk-lined cocoon covered with soil or sand. Inside the cocoon, the larva

enters diapause and will pupate a few weeks before emergence.

Interestingly, the larvas diapause can range from one to four years to help its

emergence synchronize with host flowering. Based on Pellmyrs unpublished data,

very high fruit set during mass flowering episodes in yucca populations that then

effectively cease flowering almost completely for several years suggests that the

moth larvae are capable of diapausing for several years as well, and that there are

unidentified cues that trigger completion of the moths development and adult

emergence [4].

MostTegeticula species, including antithetica, are monophagous, and the

adult moths only live for a few days, so they must access the plant during the short

flowering period. This indicates that moth populations would have to be locally

adapted for the flowering periods their specific hosts [4].


6/8

Figure 7: Female Tegeticula oviposition into a Joshua tree flower and a cross section of the floral

pistil showing the path of the moths ovipositor. The female ovipositor first cuts through the stylar

wall then pushed down the stylar canal to the ovules.

(Video)http://www.denimandtweed.com/2009/10/video-of-yucca-pollination.htmlVideo: A yucca moth laying eggs, then actively pollinating a yucca flower.

Interesting Biology

As mentioned above, Yucca moths have played a significant role in scientific

research because their unique relationship with yucca plants provides a rare

opportunity to study coevolution. While there are many examples in nature of

mutualistic relationships between plants and insects, coevolution is particularly

rare to find (and prove) because it requires reciprocal selective forces between two

species. If the specific, beneficial traits are to signify coevolution, they have to have

developed as a result of the two species interactions and not any extrinsic forces.Tegeticula and Yucca brevifolia are believed to have coevolved because the

yucca plants rely exclusively on the moths for pollinationwhich actively pollinate

the yucca flowers they will ovipositand the larvae feed exclusively on the

developing seeds. The moths and plants physiological traits are intertwined

because the moth has an exclusively sized ovipositor and only an active pollinator

like Tegeticulacan pollinate the plant. The females ovipositor must be long enough

to reach the ovules but not so long as to injure them, as seeds would not develop to

feed the larvae [5]. Coevolution acting on the partners should favor matching

between the length of the ovipositor and the flowers stylar canal [2]. This is

because the female moth only pollinates the flower after successfully ovipositing her

eggs.The two species coevolve because any morphological change in the

reproductive structures of one species forces a reciprocal selective force on the

other. For example, if genetic drift permits the ovipositor length in a population of

moths to shorten, then the only yucca plants that will get pollinated and reproduce

are the ones with shorter stylar canals. Here, the change in one species population

forces a change in the other species population, and vice versa. Overtime, enough

changes can occur where two species become entirely dependent on each other for


7/8

survival and if the two species dont evolve with each other, than the populations

will go extinct.

Godsoe, et al. (2008) presented convincing evidence for this coevolution by

showing the exclusive relationship between Tegeticula antithetica (and synthetica)

and their respective populations ofYucca brevifolia. Perhaps most importantly,

Godsoe et al. showed that only the reproductive features of the moths and plantshave been evolvingovipositor length and floral characters, respectivelyand not

body size or vegetative features, respectively. This indicates that only reciprocal

sexual selection, and not extrinsic forces (such as climate, etc.), has been acting on

the evolution of the two species.

Like other organisms with specialized hosts, the ability to specialize can

reduce competition. Tegeticulamoths dont have to compete with numerous other

populations of varying species for locations to lay their eggs, and Yuccabrevifolia

plants dont have the stress of too many insect populations exploiting its seeds.

References

[1] Pellmyr, O. and Segraves, K. A. 2003. Pollinator Divergence within an Obligate

Mutualism: Two Yucca Moth Species (Lepidoptera; Prodoxidae: Tegeticula) on the

Joshua Tree (Yucca brevifolia; Agavaceae). Ann. Entomol. Soc. Am. 96(6): 716-722

[2] Godsoe, W., Yoder, J. B., Smith, C. I., and Pellmyr, O. 2008. Coevolution and

Divergence in the Joshua Tree/ Yucca Moth Mutualism. The American Naturalist.

171(6): 816-823.

[3] Pellmyr, O., Thompson, J. N., Brown, J. M., Harrison, R. G. 1996. Evolution of

Pollination and Mutualism in the Yucca Moth Lineage. The American Naturalist.

148(5): 827-847.

[4] Pellmyr, O. 2003. Yuccas, Yucca Moths, and Coevolution: A Review. Annals of the

Missouri Botanical Garden. 90(1): 35-55


8/8

[5] Pellmyr, O., and C. J. Huth. 1994. Evolutionary stability of mutualism between

yuccas and yucca moths. Nature. 372: 257-260.

Figure 1: The yucca moth

by: Grand Canyon Trust Volunteers (Flickr)

http://www.flickr.com/photos/grand_canyon_trust/4627481885/

Figure 2: Pellmyr, O. and Segraves, K. A. 2003.

Figure 3: Godsoe, et al. 2008.





Documents

Tegeticula antithetica - Yucca Moth