Limits...
A novel technique for identifying the instar of field-collected insect larvae.

Sasakawa K - PLoS ONE (2013)

Bottom Line: The chief advantage of this technique is that the instar can be identified even when only one specimen is available per species if classification functions are determined for groups to which the focal species belongs.Similar classification functions should be created for other insect groups.By using those functions together with molecular species identification, future studies could include larval stages as well as adults.

View Article: PubMed Central - PubMed

Affiliation: Department of General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan. cksasa@mail.ecc.u-tokyo.ac.jp

ABSTRACT
Many field studies of insects have focused on the adult stage alone, likely because immature stages are unknown in most insect species. Molecular species identification (e.g., DNA barcoding) has helped ascertain the immature stages of many insects, but larval developmental stages (instars) cannot be identified. The identification of the growth stages of collected individuals is indispensable from both ecological and taxonomic perspectives. Using a larval-adult body size relationship across species, I present a novel technique for identifying the instar of field-collected insect larvae that are identified by molecular species identification technique. This method is based on the assumption that classification functions derived from discriminant analyses, performed with larval instar as a response variable and adult and larval body sizes as explanatory variables, can be used to determine the instar of a given larval specimen that was not included in the original data set, even at the species level. This size relationship has been demonstrated in larval instars for many insects (Dyar's rule), but no attempt has been made to include the adult stage. Analysis of a test data set derived from the beetle family Carabidae (Coleoptera) showed that classification functions obtained from data sets derived from related species had a correct classification rate of 81-100%. Given that no reliable method has been established to identify the instar of field-collected insect larvae, these values may have sufficient accuracy as an analytical method for field-collected samples. The chief advantage of this technique is that the instar can be identified even when only one specimen is available per species if classification functions are determined for groups to which the focal species belongs. Similar classification functions should be created for other insect groups. By using those functions together with molecular species identification, future studies could include larval stages as well as adults.

Show MeSH
Schematic diagram showing analyses of species with n larval instars.On the adult size–larval size plane, “areas” of larval instars are not expected to overlap with each other (A) because among species, species with larger adult sizes have larger larval sizes (arrow 1), and within species, older larvae have larger body sizes (arrow 2). Using this adult size–larval size relationship (B), the instar of a larval sample that was not included in the data set can be identified based on larval size (measured from the specimen; arrow 3) and expected adult size (obtained from conspecific adult specimens or the literature) after molecular methods are used to identify the species of the larval sample; arrow 4). Dotted lines indicate boundaries between instar areas. Note that this diagram is conceptual; in practical analyses (discriminant analyses), the “area” of each larval instar cannot be represented two-dimensionally.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3585218&req=5

pone-0057836-g001: Schematic diagram showing analyses of species with n larval instars.On the adult size–larval size plane, “areas” of larval instars are not expected to overlap with each other (A) because among species, species with larger adult sizes have larger larval sizes (arrow 1), and within species, older larvae have larger body sizes (arrow 2). Using this adult size–larval size relationship (B), the instar of a larval sample that was not included in the data set can be identified based on larval size (measured from the specimen; arrow 3) and expected adult size (obtained from conspecific adult specimens or the literature) after molecular methods are used to identify the species of the larval sample; arrow 4). Dotted lines indicate boundaries between instar areas. Note that this diagram is conceptual; in practical analyses (discriminant analyses), the “area” of each larval instar cannot be represented two-dimensionally.

Mentions: Among related insect species, species with a larger adult body size are expected to have a larger larval body size in a given instar (Arrow 1: Fig. 1A). In each species, older larvae must have larger body sizes (Arrow 2: Fig. 1A). Thus, in a data set composed of related species, one assumes that “areas” for each larval instar on an adult size–larval size plane do not overlap with each other (Fig. 1A). Also, in using this adult size–larval size relationship, one also expects that the instar of a larval sample that was not included in the original data set can be identified based on information about larval and adult sizes (Fig. 1B). Information on larval size can be obtained by measuring the larval specimen. Information on adult size can be obtained through molecular species identification and subsequent measurements of conspecific adult specimens or by using published values. Consequently, the instar of a larval sample can be identified if samples are available for morphological measurements and molecular analyses. Here, this method of identifying larval instar using molecular species identification and morphometric analysis was performed via discriminant analyses.


A novel technique for identifying the instar of field-collected insect larvae.

Sasakawa K - PLoS ONE (2013)

Schematic diagram showing analyses of species with n larval instars.On the adult size–larval size plane, “areas” of larval instars are not expected to overlap with each other (A) because among species, species with larger adult sizes have larger larval sizes (arrow 1), and within species, older larvae have larger body sizes (arrow 2). Using this adult size–larval size relationship (B), the instar of a larval sample that was not included in the data set can be identified based on larval size (measured from the specimen; arrow 3) and expected adult size (obtained from conspecific adult specimens or the literature) after molecular methods are used to identify the species of the larval sample; arrow 4). Dotted lines indicate boundaries between instar areas. Note that this diagram is conceptual; in practical analyses (discriminant analyses), the “area” of each larval instar cannot be represented two-dimensionally.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585218&req=5

pone-0057836-g001: Schematic diagram showing analyses of species with n larval instars.On the adult size–larval size plane, “areas” of larval instars are not expected to overlap with each other (A) because among species, species with larger adult sizes have larger larval sizes (arrow 1), and within species, older larvae have larger body sizes (arrow 2). Using this adult size–larval size relationship (B), the instar of a larval sample that was not included in the data set can be identified based on larval size (measured from the specimen; arrow 3) and expected adult size (obtained from conspecific adult specimens or the literature) after molecular methods are used to identify the species of the larval sample; arrow 4). Dotted lines indicate boundaries between instar areas. Note that this diagram is conceptual; in practical analyses (discriminant analyses), the “area” of each larval instar cannot be represented two-dimensionally.
Mentions: Among related insect species, species with a larger adult body size are expected to have a larger larval body size in a given instar (Arrow 1: Fig. 1A). In each species, older larvae must have larger body sizes (Arrow 2: Fig. 1A). Thus, in a data set composed of related species, one assumes that “areas” for each larval instar on an adult size–larval size plane do not overlap with each other (Fig. 1A). Also, in using this adult size–larval size relationship, one also expects that the instar of a larval sample that was not included in the original data set can be identified based on information about larval and adult sizes (Fig. 1B). Information on larval size can be obtained by measuring the larval specimen. Information on adult size can be obtained through molecular species identification and subsequent measurements of conspecific adult specimens or by using published values. Consequently, the instar of a larval sample can be identified if samples are available for morphological measurements and molecular analyses. Here, this method of identifying larval instar using molecular species identification and morphometric analysis was performed via discriminant analyses.

Bottom Line: The chief advantage of this technique is that the instar can be identified even when only one specimen is available per species if classification functions are determined for groups to which the focal species belongs.Similar classification functions should be created for other insect groups.By using those functions together with molecular species identification, future studies could include larval stages as well as adults.

View Article: PubMed Central - PubMed

Affiliation: Department of General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan. cksasa@mail.ecc.u-tokyo.ac.jp

ABSTRACT
Many field studies of insects have focused on the adult stage alone, likely because immature stages are unknown in most insect species. Molecular species identification (e.g., DNA barcoding) has helped ascertain the immature stages of many insects, but larval developmental stages (instars) cannot be identified. The identification of the growth stages of collected individuals is indispensable from both ecological and taxonomic perspectives. Using a larval-adult body size relationship across species, I present a novel technique for identifying the instar of field-collected insect larvae that are identified by molecular species identification technique. This method is based on the assumption that classification functions derived from discriminant analyses, performed with larval instar as a response variable and adult and larval body sizes as explanatory variables, can be used to determine the instar of a given larval specimen that was not included in the original data set, even at the species level. This size relationship has been demonstrated in larval instars for many insects (Dyar's rule), but no attempt has been made to include the adult stage. Analysis of a test data set derived from the beetle family Carabidae (Coleoptera) showed that classification functions obtained from data sets derived from related species had a correct classification rate of 81-100%. Given that no reliable method has been established to identify the instar of field-collected insect larvae, these values may have sufficient accuracy as an analytical method for field-collected samples. The chief advantage of this technique is that the instar can be identified even when only one specimen is available per species if classification functions are determined for groups to which the focal species belongs. Similar classification functions should be created for other insect groups. By using those functions together with molecular species identification, future studies could include larval stages as well as adults.

Show MeSH