I



Entomology: May 19, 2006

Reproduction and Development 1

I. Male: major parts (located in posterior portion of the abdomen)

A. Testes

1. Composed of testicular follicles encased in 2 layers

a. Type/functions of the two encasing layers (know!)

b. Functions of follicular tissue itself (know!)

c. Different sections of each follicle have sperm in different stages of development.

▪ Where are the most fully-formed sperm located?

B. Vas deferens

1. muscular, allows for propulsion of semen

C. Seminal vesicles

1. storage of sperm, often in the form of spermatophores (sperm packets) used to transfer sperm to females

a. In which insect orders are you least likely to find spermatophores?

b. Note that other arthropods use spermatophores for sperm transfer

D. Ejaculatory duct

1. Sperm forcibly ejected during mating

E. Gonopore

1. opening to outside

F. Accessory glands

1. secrete chemicals directly related to sperm

a. Examples…

2. secrete additional chemicals that affect the female

a. Five different types of chemicals described. Know!

b. NOTE: These chemicals appear to act by passing from the male’s secretions into the female’s hemolymph, where they essentially act as hormones.

G. Penis (a.k.a. “aedeagus”)

A Males of closely related species often have very different genitalia.

B Adaptive value?

H. Accessory copulatory structures

C A variety of accessory copulatory structures aid in clasping females and in sperm deposition

D Examples…

1. Odonata penises have specialized “scoopers”

a. What do they scoop?

b. .How does the location of its penis differ from most insects?

II. Female: Major parts

A. Ovaries:

1. Site of egg production and maturation

B. Ovarioles

1. Ovaries composed of multiple ovarioles each encased in a layer of epithelium

a. Associated tracheae pipe in oxygen to meet energy demands

b. Muscle sheaths allow for movement of eggs

c. Number of ovarioles varies: 2000 in some queen termites

2. Each ovariole has eggs in different stages of development.

a. Adaptive value?

3. Two major sections: germarium and vitellarium

a. Germarium

▪ Major function?

b. Vitellarium

▪ Major function?

▪ Organization (i.e. where are the most mature eggs located)?

▪ What is a follicle (structure/function)?

▪ NOTE: All eggs in the lowermost segment of each ovariole can be fertilized and deposited simultaneously

C. Oviducts

1. lateral oviducts and common oviduct; deposit eggs into vagina.

D. Spermatheca

1. sperm storage organ; allows for decoupling of mating and fertilization

E Sperm can be stored from weeks to years

F Example: honeybees

2. Female controls timing of fertilization by controlling release of eggs and sperm into the vagina

E. Accessory glands/spermatheca glands

1. secretion of substances which hold eggs together and/or glue them to substrate

2. In tsetse flies, secrete a nutritious substance for nursing larvae.

F. Vagina

1. Common chamber into which oviducts, spermatheca and accessory glands empty

G. Ovipositors

1. A variety of structures specialized for the particular egg-laying behavior and egg/larval habitat.

a. Some examples

III. Control of egg maturation/vitellogenesis (Fig. 5.7).

A. Egg production in most insects is food-limited. The entire process of egg development is stimulated by feeding.

1. Adaptive value?

2. What aspects of feeding, specifically, set the egg maturation process in motion?

B. Brain neurohormones are released from protocerebrum.

1. Stored and then released by the corpora cardiaca.

a. These stimulate the ovaries to release ecdysone.

▪ The ecdysone then stimulates the fat body to produce vitellogenin, the precursor to the vitellin (yolk)

2. Act on the corpora allata (apparently not stored and released, but act directly on c.a. cells via hemolymph after release from c.c.)

a. These stimulate the corpora allata to release a hormone (JH?) that stimulates the ovaries to deposit yolk (vitellin).

C. How is it possible for egg maturation/egg-laying to be out of synch with mating?

IV. Control of sperm production

A. Not as well-studied, but it appears that JH and ecdysone play a role, as in egg production/vitellogenesis

Basics of mating

A Locating mates

B Pheromones

C Example: moths (best-studied)

D Visual cues

E Firefly (Coleoptera!) "Morse code"-like signals emitted from light organ on ventral abdomen

F Species ID encoded in flash pattern, shape of signal, and flight height

G Type 1: Females flash signal to attract male

H Type 2: Males flash, females choose and return own "I'm here" flash.

I Predatory females may "trick" males of other species…

J Swarming (usually by males)

K Ex: Ephemeroptera, Trichoptera, Diptera

L Females are attracted to the swarms, and fly in and mate.

M Acoustic cues

N Ex: Orthoptera, Homoptera, Diptera

O Copulation

P Internal fertilization

Q Sperm/spermatophore deposited into vagina, or directly into spermatheca

R Male actions to assure his own sperm fertilize the eggs:

S Lepidoptera: Anti-aphrodisiacs

T Hymenoptera: Mating plugs

U Mantodea: Prolonged mating or feeding

V Odonata: sperm scooping structure.

W Fertilization:

X Eggs fertilized as they move through the oviduct and past the spermatheca

B. Parthenogenesis

1. Unfertilized eggs develop into offspring

a. Depending upon precise mechanism, these offspring can be diploid or haploid; in the Hymenoptera, they are always haploid and male.

Y Fate of eggs/offspring after fertilization

Z Oviparity: eggs laid by female (oviposition = use of ovipositor to precisely position eggs in suitable habitat): most insects

AA Ovoviparity: eggs retained by female, but nutrition comes from egg. Young released as larvae

AB Sheep bot fly: Deposits larvae into sheep nostrils

AC Viviparity: Embryos retained by female, and nutrition also comes directly from mother, not egg.

b. Occurs in some aphids and in tsetse flies

Study questions

NOTE: Be sure to also answer questions posed in the body of the outline itself!

1. Be able to label the basic parts of the male and female reproductive systems (see Figure 5.1a, 5.4a, with emphasis on those parts discussed in class.) Also know the functions of these structures.

2. Name the two major categories of substances secreted by the accessory glands within the male reproductive system. Also, be able to provide examples of each type (several examples were given for chemicals that affect the female…).

3. Within the ovariole, where are the most mature eggs located? What does having eggs in different stages of development allow the female to do?

4. What is the key factor which limits egg production in insects?

5. Be able to describe the basics of hormonal control of egg maturation and vitellogenesis. Study and understand Figure 5.7. You should focus on:

Effect of food (especially protein): When food is adequate, to where is a "message" sent?

Identify the major hormones involved

Know where each of the key hormones is synthesized and where it is released. (HINT: brain hormone [BH] is a little tricky. It is produced in the protocerebrum, sent to the corpora cardiaca via the same neurons in which it is produced, and released from the cc into the hemolymph. Brain hormone also affects the corpora allata via the hemolymph.

Know the major effect(s) of each of these key hormones as relates to egg production

What is vitellogenin and where is it synthesized? What is vitellin?

6. Is fertilization in insects internal or external? Where in the female reproductive system does fertilization occur?

7. Explain how it is possible for the process of fertilization to be uncoupled from the process of mating, including all pertinent structures in your explanation.

8. What types of cues do insects use to locate mates? You should be able to give examples for each cue (Example: general cue type is visual. More specifically, fireflies communicate mating signals with flash patterns unique to each species.)

9. What is meant by "sperm precedence?"

10. Describe several methods used by males to assure that it is their sperm, and not another male’s sperm, that fertilizes the female's eggs.

11. Explain the differences between oviparity, ovoviparity and viviparity in terms of:

whether the egg is retained by the female

whether the egg is nurtured by yolk or by other sources of nutrition from the female.

12. What is parthenogenesis?

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