Teleopsis+dalmanni

//Teleopsis dalmanni// (Wiedemann, 1830)



** Overview ** With eyes at the tip of their eye stalk, //Teleopsis dalmanni// and members of Diopsinae definitely make into the list of most bizarre-looking animals on earth. This group of flies has sparks research interest in the physiology, development and evolutionary mechanism leading to the eye stalks. //T. dalmanni// is probably the most widely studied particularly in the field of sexual selection leading to sexual dimorphism in this species, where males and females differ in appearance.

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= The Eye Stalk =

The most striking feature of //Teleopsis dalmanni// and other members of Diopsinae is definitely the lateral head projection (the “eye stalk”), which bore the eyes and the antenna. The eye stalk is derived from the posterior half of the eye-antennal disc (Figure 1). Visual fields of the compound eyes of //Teleopsis dalmanni// overlap 3-4 mm in front of their eyes, making it possible for them to perceived depth of objects placed within the overlapping region.

Shortly after eclosion, before their structures hardened, //T. dalmanni// ingest air thorough their oral cavity, and pump it to the tips to their stalk through a duct in the head, thereby elongating their stalk. Watch the video to see an newly-emerged adult flies pumping their eye stalks!

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It should be noted that Stalk-eyed flies are not the only group of Dipteran flies that posses eye stalks (Figure 2; click here for examples of Dipteran with eye stalk). However, they are unique by having the antenna near the end of the eyes stalk, next to the eye instead of in the facial region (Figure 3). .

= Sexual dimorphism and sexual selection in //Teleopsis dalmanni// = //Teopsis dalmanni// display high degree of sexual dimorphism (Figure 4). The eye span of males is longer than its body length while in females, it is shorter. Therefore, it is possible to tell apart sexes base on the ratio of eye span to body length. Baltic amber fossils revealed sexual dimorphism of eyestalk is present in the ancestral state of Diopsinae, and this trait is maintained through time by sexual selection via female mate choice and male-male interaction. There is also a difference in head shape, with males having smaller eye bulbs, thinner stalks, and smaller head than females.

** Female mate choice: Why does females prefer males with longer eye span? **

media type="custom" key="21508134" align="center" Figure 5: Female Teleopsis dalmanni [Courtesy of Rob Knell, used with permission]

Females //Teleopsis dalmanni// (Figure 5) were likely to be attracted to sites controlled by male with larger eye span, and there is a genetic basis for females to prefer males with longer eye stalk , thereby creating a selection force for longer eye stalks in males.

Under the handicap hypothesis of mate choice, female judge the quality of males through sexual ornamentation, such as the eye stalk, which are costly to develop. A high-quality male will be able to support longer eye stalks which are costly despite poor condition. It was found that males with larger eye span have bigger accessory glands, testes, and hence are able to mate more frequently than males with smaller eye span. This is beneficial for females as more frequent mating increase the number of sperm received, alleviating the problem of sperm shortage faced by females //Teleopsis dalmanni.//

(Click here for more information on sperm shortage in females).

However, a study demonstrates that females //Teleopsis dalmanni// actually laid less fertile eggs after mating with males with larger eye span, indicating that sperms from males with larger eye span have superior competitive ability but not superior fertilization ability compared to their smaller counterparts. Despite this, females still gain direct benefit from mating with larger eye span males by having more sperm transfer per copulation.

** Limitation for length of eye span: Why don't males have longer eye stalks? **

Since males with longer eye span gain benefits of having more mating opportunities, there is a strong sexual selection force for increasing longer eye stalks in males. However, there is a limit in the length of the eye stalks.The process of developing longer eye stalk could create developmental problems in the larvae stage, leading to high larvae mortality rate in the pupae stage. Longer eye stalk also requires longer development time, which increase the exposure to toxic metabolites produced by conspecific larva, as well as to predators and parasites. Therefore, the length of male eye stalk is maintain by natural selection opposing the force of sexual selection.

** Adaptation following longer eye stalk in males **

With longer eyestalk, males //Teleopsis dalmanni// experiences more drag force and moment of inertia during flight. Hence, other traits have coevolved with the longer eyestalk in males. To enhance their flight performance and survival ability, males have larger wings than females. Males also generate stronger moments per wing beat, which probably improve the turning performance during flight to compensate for the higher moment of inertia. Moreover, it was also found that despite the larger moment of inertia of the head, males //Teleopsis dalmanni// could match the head saccade of females, suggesting that the longer eye stalk is support by an adaptation of the neck apparatus to rotate the wider head.

** Male mate choice: Do males choose their mates too? **

Study shows that males //Teleopsis dalmanni// do not choose their mate on their mating status (virgin or mated). However, they produced larger spermatophore when mated to large-eyespan females, suggesting that males might strategically allocate more ejaculation to females with larger eye span. This is because female eye span is found to be an accurate predictor of fecundity. Female with larger eye span can produce more eggs than smaller females and after a single mating, females with larger eye span laid more fertile eggs after than smaller eye span females.

= Mating system = media type="custom" key="21508164" align="center" Figure 6: A pair of copulating Teleopsis dalmanni. Note that the front legs of the male. are resting on the scutellum spines of the female.[Image embedded from Flickr, permission pending from Dr. Samuel Cotton]

The mating system of //Teleopsis dalmanni// is characterized by:

1. Short copulation duration: Copulation usually lasted less than a minute

2. Frequent mating in both sexes: In the laboratory, males are capable of mating up to 10 times per hour; while females are capable of mating six times per hour up to 40 times per day!

(Click here to learn why they mate so frequently!)

Between dusk and dawn, //Teleopsis dalmanni// individuals form nocturnal aggregation on exposed root hairs.The number of females in each aggregation varies[9], while there is normally only a single male or occasionally, two males. This is because during the process of aggregation, males will engage in aggressive competition to displace each other to become owner of the site. Owner of aggregation sites will be rewarded with mating with multiple females in the aggregation. Sometimes, lone males would sneak mate with females in other males’ harem.Watch two //T.dalmanni// fight in the video (Embed from Flickr, pending permission from Dr. Samuel Cotton) below:

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(Click here to see what determines the outcomes of an aggressive interaction!)

Interestingly, field studies in Malaysia reveals that most dimorphic species of Stalk-eyed flies, and none of the monomorphic species, where males and females look alike, form this nocturnal aggregation form this aggregation. This suggest that the behavior of aggregating and intrasexual competition between males, besides sexual selection, is a selection force for sexual dimorphsim in the Stalk-eyed flies.

= Morphology = ** Adult morphology **

In general, adult //T.dalmanni// are reddish-brown in color, with head, thorax and legs covered with dense hair. They posses eye stalks, and the thorax has long scutellum spines (Figure 7).


 * < ** Head ** ||< 1. Outer vertical bristle black twice as long as width of eye-stalk in the middle.

2. Covered with brown hairs.

3. Inner vertical bristle up to 4.5–5 times as long as width of eye-stalk in the middle; on a small tubercle.

4. No facial teeth, edge rounded.

||
 * < ** Thorax ** ||< 1. Scutellar spines up to 4 times as long as length of scutellum.

2. Shiny, reddish-brown, without extensive pollinosity.

||
 * < ** Legs: Femur ** ||< 1. Covered with hairs (shorter than those on the head).

2. With incision near.

3. With rows of peg-like black tubercles in front.

4. Mid femur distally swollen.

||
 * < **Male Genitalia** ||< 1. Long setae (bristles) on the epandrium(in red) and the cerci (in yellow).

2. Broad surstyli (in blue).

|| **Table** **1**: Gross morphological description of //Teleopsis dalmann// //i//.

The wing morphology of this species is not describe here as specimens collected from different locality showed considerable variance (Refer here). For a more detailed adult morphology, please refer to here.

** Egg morphology **

Studies on the egg morphology of Stalk-eyed flies using Scanning Electron Microscope (SEM) demonstrated that egg morphology is useful for identification purposes and for cladistic analysis.

** Dichotomous Key **



= Taxonomy = ** Type information ** A holotype (Type specimen) is the specimen in which the description of a species is based on. Holotypes for resolving taxonomic confusion, i.e when a 'species' is described under different name (synonyms); or when different species are described as the same species. Holotype location of Teleopsis dalmanni: Museum of Westermann

Type locality: Jakarta, Indonesia

** Taxonomic history **

There are 270 species of Stalk-eyed flies, grouped in 14 genus recorded.//Teleopsis dalmanni// was first described as Diopsis dalmanni by Wiedemann (1830) in Aussereuropäische Zweiflügelige Insekten (Volume t. 2), and was later renamed as //Cyrtodiopsis dalmanni,// classified under Cyrtodiopsis Frey, 1928. Results from cladistic analysis using both morphological and DNA characteristic later merged Teleopsis and Cyrtodiopsis together and due to naming priority, all Cyrtodiopsis species is renamed to Teleopsis. Hence, what was known as //Cyrtodiopsis dalmanni// is now // Teleopsis dalmanni. //

**Synonyms** //Diopsis dalmanni// Wiedemann, 1830 //Diopsis attenuata// Doleschall, 1856 //Diopsis lativola// Rondani, 1875 //Diopsis latimana// Rondani, 1875 //Teleopsis truncata// Brunetti, 1928 //Cyrtodiopsis dalmanni// (Wiedmann), Frey 1928 Valid name: //Teleopsis dalmanni// (Wiedmann, 1830)

The list of synonyms probably resulted from the morphologically highly variable Teleopsis dalmanni. There appear to be variation in wing pattern (Figure 14) from specimen collected from different locality (Study of Diopsidae) [21]. Variation in wing pattern could be a result of poor preservation of specimen, or could be corresponding to variation in habitat.



= Phylogeny = Phylogenetic analysis using both morphology and molecular data revealed that //Teleopsis dalmanni// are sister species to //Teleopsis whitei// (Figure 15),which also display sexual dimorphism. The distribution of both species overlap each other (sympatric species), but are reproductively isolated[3]. The two species can be distinguish base on the foreleg morphology as described in the morphology session: //Teleopsis whitei// do not have the incision in the femora of the front leg.



= Distribution = ** Singapore **

Till date, there is no proper studies in surveying the diversity of Stalk-eyed flies in Singapore, but they have been photographed by photography enthusiasts in MatRitchie Reservoir Park, Dairy Farm (Figure 16), Singapore Botanic Garden, Bukit Timah and Nee Soon Swamp Forest (MAP). //Teleopsis dalmanni// could be found in Central Catchement area. Stalk-eyed flies are generally found at shady areas, near edge of forest streams, or in wet muddy area with rotten vegetation in proximate (Figure 17).

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 * Map 1 ** : The location of Stalk-eyed flies photographed in Singapore.

** Global distribution ** Most of the described Stalk-eyed flies species are found in the Old World with the Afrotropical region having the most species. There is only two species found in the New World and are found in temperate North America. The distribution of //Teleopsis dalmanni// and other Teleopsis species are restricted to South East Asia. //Teleopsis dalmanni// have a wide distribution in this geographical range. They were collected from Indonesia, Thailand, Malaysia, Borneo, and Phillipines. This species was first discovered by Wiedmann in Jakarta (type locality) in 1830.

= Biology = 23] ** Diet **

Adult //Teleopsis dalmanni// diet consists of yeast, mold and fungi found on rotting vegetative matter. Larvae of this species are saprophagous and feed on decaying matter.

** Daily activity pattern **

//Teleopsis dalmanni// diet consists of yeast, mold and fungi found on rotting vegetative matter during the day. Field observation reveals that this species normally act aggressively towards conspecific of both sexes during the day. From dusk to dawn, the flies will form aggregations on threadlike plant structures, for example, exposed root hairs, where males will compete to displace each other from the aggregation, and copulation occur (See mating system). In the field, marked flies were often observed on the same threads, an indication of place memory and place constancy [3]

** Life cycle **

Stalk-eye flies shared the same general life history pattern (Figure 18), although fecundity, age of sexual maturity and longevity varies among species. Adult males // Teleopsis dalmanni // require about 25 days to reach sexual maturity after emerging from pupae stage; while females require 22 days. After successful copulation, females // Teleopsis dalmani // lay on average 4-6 eggs per day and may continue laying eggs for many months. The eggs require 1-3 days to hatch. Larvae stage range from 10 days to several weeks, depending on temperature of environment and food quality. Late-instar larvae empty their gut content in a process called gut-purge, and enter pupation state. In food-depriving environment, pupation might occur at smaller larvae size. They typically pupate on emergent vegetation.Pupation stage last for almost a week, after which an adult fly will emerge, completing the life cycle of // Teleopsis dalmanni //.

** Life span of adults **

In laboratories, adult // Teleopsis dalmanni // can live for an average of 4 months and easily reach over 6 months. This long life span is not only observed in the laboratory: the age of field-caught Teleopsis dalmanni were estimated from pteridine eye pigments to be, on average, over 30 days, with large adults surviving over 200 days.

** Sex ration of adults **

Sex ratio of adult //Teleopsis dalmanni// are found to be female biased with a ratio of 1.187: 13]. This ratio is found in both lab culture and wild population.

= Culturing //Teleopsis dalmanni// = //Teleopsis dalmanni// can be easily cultured using cages or containers with strings suspended from the roofs to mimic root hairs, and lined with moistened kitchen towel to provide moisture. Corn puree can be provided as egg-laying substrate and food for both adult and larvae. Corn puree can be prepared by grinding the whole ears (without removing the husk) and appropriate amount of water in a food processor to make a pulp. Mold-inhibitor solution and fungicide can be added in small amount to prevent mold and fungal growth.

= High mating frequency in //Teleopsis dalmanni//: Why? = The sperms of a male //Teleopsis dalmanni// are transfer to females in a goud-shaped spermatophore (sperm package). The spermatophore of a //T. dalmanni// is relatively smaller to those of other diopsids (5% of //Teleopsis quadriguttata// ), and only occupies only a part of the vaginal cavity. This is because as the mating system of //Teleopsis dalmanni// provides males in a harem with multiple mating opportunities, hence males do not have to invest on a large spermatophore per copulation. As a result, the number of sperm transferred to females to be very low. It was found that only about 55% of eggs laid by females in the wild were fertilization 9], and fertility of females declined when there is no access to mate. These indicate that females faced sperm shortage. The problem of sperm shortage is further elevated by the presence of X-linked meiotic drive element in males //T. dalmanni// which reduces the fertilizing ability of affected males. Therefore, it is beneficial for females to mate multiple times in order alleviate the problem of sperm shortage, and to increase the number of fertile eggs. On the other hand, high mating rate is beneficial for the males too as it increases the number of eggs it can inseminate, and to gain an upper hand in sperm competition as females mate multiply and there is high incidence of sperm mixing in //T. dalmanni//.

**Limiting factors for mating frequency**

In insects, males’ accessory glands secrete products that mix with the sperms and form the casing of the spermatophore which will be transfer to females during copulation. There is a significant decrease in accessory gland length of //Teleopsis dalmanni// after mating. Hence, males need to ‘rest’ for 8 to 48 hours for their accessory gland to recover slowly. Furthermore, male mating frequency is also constrains by how rapid sperm and seminal fluid is replenish.

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= Intrasexual competition in //Teleopsis dalmanni// = media type="custom" key="21461580" align="left" width="119" height="119"

Figure 19: Two males Teleopsis dalmanni fighting. [Image embedded from Flickr, permission pending from Dr. Samuel Cotton]

Males compete for ownership of a female aggregation. The winner of the combat will be in control of the aggregation sites, increasing its reproductive success.Table 2 describe aggressive behaviors of different intensity displayed by males during an encounter, and Figure 20 describe the sequence of events during a contest between males.

** What does it takes to win? **

The length of eye stalk strongly affects the outcome of the males’ competition over a female aggregation. Males with larger eyespan, independent of body size, are more aggressive and win proportionately more aggressive interaction than males with smaller eye span6] . Males engage in aggressive interaction not only for control over site (mating opportunity) but also for food resource. It was found that during competition for food resource and territories, eye span is positively correlated with outcome of the competition and fight duration decreases as difference in males’ eye span increased. Aggressive interaction between males shows pattern of escalation with no de-escalation, and often involve physical contact but no injuries.

** Do females fight too? **

Females do fight for resources too. However, unlike the males, eye span was found not to affect the outcome of intrasexual competition between females //Teleopsis dalmanni//. Rather, it is body size that determines the outcome of a competition; with larger females more likely to win an encounter.

**Table 2**: Ethogram of aggrassive behavior observed in males //Teleopsis dalmanni.//
 * = ** Behavior ** ||= ** Description ** ||
 * Low-intensity behaviors ||
 * Approach opponent || Movement toward opponent ||
 * Line up eye stalks || Oriented with eye stalks to opponent’s in parallel function ||
 * Rear up || Use mid-and hind-legs to rise in posture ||
 * Flex and extend forelegs || Bends and flicks forelegs near own eye stalks; directed at opponent ||
 * High-intensity behaviors ||
 * Jump attack || Jumps on opponent’s dorsal side ||
 * Attack/lunge || Use forelegs in downward motion, striking at or on opponent ||
 * Tussle || Entangled with opponent, either clasping opponent’s forelegs or eye stalks ||
 * Conflict Resolution behaviors ||
 * Away || Turning away or slowly moving away from opponent ||
 * Pursue || Quickly moving after opponent while no longer facing opponent ||
 * Retreat || Quickly moving from opponent while no longer facing opponent ||
 * End || Eye stalks are no longer aligned for a minimum of 3 s or flies are at least one body length apart ||

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= Diopsinae =  Diopsinae is a taxonomic group of fly in which members posse the eye stalks. This group is nested within the Diopsidae, the Stalk-eyed flies. However, taxonomists do not agree with what constitute the Diopsidae. The traditional definition of Diopsidae includes the Centrioncinae, in which members do not have the eye stalks, and the Diopsinae. However, some taxonomists argue that the Centrioncinae should not be included in the Diopsidae, and should treat as a different group.[20] Stalk-eyed flies in this page refers to the members of Diopsidae that includes Centrioncinae.

 = References =